Method of manufacturing a semiconductor device

ABSTRACT

A semiconductor device is provided which is constituted by semiconductor devices including a thin film transistor with a GOLD structure, the GOLD structure thin film transistor being such that: a semiconductor layer, a gate insulating film, and a gate electrode are formed in lamination from the side closer to a substrate; the gate electrode is constituted of a first-layer gate electrode and a second-layer gate electrode shorter in the size than the first-layer gate electrode; the first-layer gate electrode corresponding to the region exposed from the second-layer gate electrode is formed into a tapered shape so as to be thinner toward the end portion; a first impurity region is formed in the semiconductor layer corresponding to the region with the tapered shape; and a second impurity region having the same conductivity as the first impurity region is formed in the semiconductor layer corresponding to the outside of the first-layer gate electrode, which is characterized in that a dry etching process consisting of one step or two steps is applied to the formation of the gate electrode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and a method ofmanufacturing the same, and particularly to a thin film transistor(hereinafter referred to as TFT) with a GOLD (abbreviated form of“gate-overlapped-LDD”) structure and a method of manufacturing the same.Note that the semiconductor device in this specification indicatessemiconductor devices in general the circuit of which is configured bysemiconductor devices including a TFT with a GOLD structure. Forexample, semiconductor display devices such as an active matrix liquidcrystal display device and an organic EL (abbreviated form of“electro-luminescence”) display device are included in the category ofthe semiconductor device.

2. Description of the Related Art

In semiconductor display devices, such as an active matrix liquidcrystal display device and an organic EL display device, the circuit ofwhich is configured by TFTs on a transparent insulating substrate suchas a glass substrate, a polycrystalline silicon TFT having a highfield-effect mobility has attracted attention. A polycrystalline siliconfilm applied to the polycrystalline silicon TFT has a higherfield-effect mobility of an electron or hole than a conventionalamorphous silicon film, and thus has an advantage that integration ofnot only a pixel transistor but also a driver circuit as a peripheralcircuit can be realized. Therefore, each company has been advancing thedevelopment of an active matrix semiconductor display device the circuitof which is configured by polycrystalline silicon TFTs.

In the polycrystalline silicon TFT, it has a high field-effect mobility,but on the other hand, there is observed deterioration phenomena such aslowering of the field-effect mobility or an ON current (current thatflows in an ON state) and increase in an OFF current (current that flowsin an OFF state) when the polycrystalline silicon TFT is continuouslydriven. These have been problems in terms of reliability. Thedeterioration phenomenon is called a hot carrier phenomenon, and isknown to be caused by hot carriers generated due to a high electricfield in the vicinity of a drain.

The hot carrier phenomenon is one first discovered in a MOS (abbreviatedform of “metal oxide semiconductor”) transistor which is manufactured ona semiconductor substrate, and it has been found that the cause of thephenomenon is the high electric field in the vicinity of a drain.Various basic examinations have been made for measures against hotcarriers. The MOS transistor with a design rule of 1.5 μm or less adoptsan LDD (abbreviated form of “lightly doped drain”) structure. In the LDDstructure, an n-type or p-type low concentration impurity region (n⁻region or p⁻ region) is formed in a drain end portion by utilizing agate side wall that is comprised of an insulating film, and a gradientis imparted to an impurity concentration of a drain junction, therebyrelaxing an electric field concentration in the vicinity of a drain.Here, an n-type low concentration impurity region and an n-type highconcentration impurity region are respectively called an n⁻ region andan n⁺ region, and a p-type low concentration impurity region and ap-type high concentration impurity region are respectively called a p⁻region and a p⁺ region.

However, in the LDD structure, the resistance of the low concentrationimpurity region (n⁻ region or p⁻ region) is large while a drainwithstand voltage is improved much compared with a single drainstructure. Thus, the LDD structure has a defect that a drain currentdecreases. Further, there has been the problem of a deterioration modepeculiar to the LDD in which: a high electric field region exists justunder the side wall; impact ionization becomes maximum there; hotelectrons are implanted into the side wall; and thus, the lowconcentration impurity region (n⁻ region or p⁻ region) is depleted, andthe resistance is further increased. The above-mentioned problem hasbeen tangible along with the reduction of a channel length. Thus, as tothe MOS transistor with a design rule of 0.5 μm or less, the GOLDstructure is developed in which a low concentration impurity region (n⁻region or p⁻ region) is formed so as to overlap with an end portion of agate electrode as a structure for overcoming the above-mentionedproblem, and the application of the structure to mass production hasbeen advancing.

Under the above-mentioned background, as to the polycrystalline siliconTFT manufactured on a transparent insulating substrate such as a glasssubstrate as well, the development of the LDD structure or GOLDstructure has been progressing with the purpose of relaxing a highelectric field in the vicinity of a drain, similar to the MOStransistor. The LDD structure is such that an n-type or p-type lowconcentration impurity region (n⁻ region or p⁻ region) that functions asan electric field relaxation region is formed in a semiconductor layercomprised of a polycrystalline silicon film corresponding to the outsideof a gate electrode, and a high concentration impurity region (n⁺ regionor p⁺ region) with the same conductivity as a source region or drainregion is formed outside thereof. The LDD structure concerned has anadvantage that an OFF current is small and a disadvantage that a hotcarrier suppression effect due to relaxation of an electric field in thevicinity of a drain is small. On the other hand, in the GOLD structure,a low concentration impurity region (n⁻ region or p⁻ region) is formedso as to overlap with an end portion of a gate electrode. Thus, the GOLDstructure has an advantage that a hot carrier suppression effect islarge and a disadvantage that an OFF current increases, in comparisonwith the LDD structure.

As described above, each of the LDD structure and the GOLD structure hasgood points and bad points. Thus, in the actual semiconductor displaydevice, from the viewpoint of quality improvement of the semiconductordisplay device, there is examined the effective combination in circuitconfiguration of a low OFF current characteristic of the LDD structureand a high hot carrier resistance of the GOLD structure. Specifically,in the case of a pixel TFT in a pixel region, the gate structure ispreferable in which importance is placed on reduction in an OFF currentvalue rather than high reliability to a hot carrier, and thus, the LDDstructure having a low OFF current characteristic is suitable. On theother hand, in the case of a peripheral circuit consisting of a drivercircuit, the gate structure is preferable in which importance is placedon high reliability to a hot carrier rather than a low OFF currentcharacteristic, and thus, the GOLD structure having high hot carrierresistance is suitable. Therefore, the recent semiconductor displaydevice the circuit of which is configured by a polycrystalline siliconTFT has a tendency that a pixel TFT in a pixel region is comprised of anLDD structure TFT, and a peripheral circuit is comprised of a GOLDstructure TFT.

Note that, as to a known example on an n-channel polycrystalline siliconGOLD structure TFT, the structure and basic characteristics of then-channel GOLD structure TFT are disclosed in Mutsuko Hatano, HajimeAkimoto, and Takeshi Sakai, IEDM97 TECHNICAL DIGEST, p523-526, 1997. Inthe structure of the GOLD structure TFT examined here, a gate electrodeand a side wall for LDD are formed of polycrystalline silicon, an n-typelow concentration impurity region (n⁻ region) that functions as anelectric filed relaxation region is formed in an active layer (formed ofpolycrystalline silicon) just under the side wall for LDD, and a highconcentration impurity region (n⁺ region) with the same conductivitywhich functions as a source region or drain region is formed outsidethereof. As to the basic characteristics, a large drain current isobtained together with relaxation of a drain electric field, and a largesuppression effect against a drain-avalanche-hot-carrier is obtained incomparison with the general LDD structure TFT.

Further, as to another example on the GOLD structure TFT, there aredisclosed in JP 7-202210A, “a thin film transistor with an LDD structurewhich is characterized in that a gate electrode takes a structure of twolayers having different widths, the upper layer of which has a smallerwidth than that of the lower layer” and “a method of manufacturing athin film transistor with an LDD structure which is characterized inthat: there is formed a gate electrode with a structure of two layershaving different widths, the upper layer of which has a smaller widththan that of the lower layer; and then, ions are implanted in a regionthat serves as a source or a drain using the gate electrode as a mask”.In JP 7-202210A concerned, there is described that “an accelerationvoltage and an ion implantation amount at the time of ion implantationare appropriately selected, whereby an n⁺ region (or p⁺ region) in aregion with no gate electrode, an n⁻ region (or p⁻ region) in a regiononly with a layer of a gate electrode, and an intrinsic (state with noion implantation) region in a region with two layers of a gate electrodeare simultaneously formed at the time of ion implantation”. There isprovided a structure in which an n⁻ region (or p⁻ region) that is anelectric field relaxation region overlaps with an end portion of a gateelectrode, and therefore, the invention relating to the GOLD structureTFT is substantially disclosed.

In JP 2001-281704A, there is disclosed a method of manufacturing a GOLDstructure TFT, including forming a gate electrode with a laminatestructure of two layers and performing a dry etching process consistingof a large number of process steps comprising taper etching andanisotropic etching.

In JP 7-226518A, there is disclosed the invention in which: a filmformed of a material constituting a gate electrode is formed; a mask isformed on the film formed of a material constituting the gate electrode;side etching is performed to the film formed of a material constitutingthe gate electrode to form a gate electrode having a smaller width thanthat of the mask; and an impurity is introduced into a semiconductorfilm to form an LDD region.

The development of the GOLD structure TFT excellent in hot-carrierresistance is being progressed in out company as well, and the structureof a typical GOLD structure TFT is described below with reference toFIGS. 3A and 3B. FIG. 3A is a sectional view of a GOLD structure TFTonly having the Lov region. FIG. 3B is a sectional view of a GOLDstructure TFT having both an Lov region and an Loff region. Note that,in this specification, an electric field relaxation region that overlapswith a gate electrode is referred to as an Lov region, and an electricfield relaxation region that does not overlap with a gate electrode isreferred to as an Loff region.

In the structure of the GOLD structure TFT only having an Lov region(FIG. 3A), on a transparent insulating substrate 301, an island-likesemiconductor layer 302, a gate insulating film 303, and a gateelectrode 304 are laminated from the side closer to the substrate 301,and a source region 305 and a drain region 306 are formed in theisland-like semiconductor layer 302 outside the gate electrode 304. Theabove GOLD structure TFT is characterized in that: the gate electrode304 is constituted of a first-layer gate electrode 304 a and asecond-layer gate electrode 304 b; the first-layer gate electrode 304 ais formed longer in size in a channel direction than the second-layergate electrode 304 b; electric field relaxation regions, that is, Lovregions 307 are formed in the island-like semiconductor layer 302corresponding to the regions of the first-layer gate electrode 304 awhich are exposed from the second-layer gate electrode 304 b; and thesource region 305 and the drain region 306 are formed in the island-likesemiconductor layer 302 corresponding to the outside of the gateelectrode 304.

In the GOLD structure TFT with the above structure, the Lov region 307is an electric field relaxation region formed so as to overlap with anend portion of the first-layer gate electrode 304 a, and consists of ann-type or p-type low concentration impurity region (n⁻ region or p⁻region). The Lov region 307 has a concentration gradient the impurityconcentration of which gradually increases toward the source region 305or the drain region 306 which is an n-type or p-type high concentrationimpurity region (n⁺ region or p⁺ region), and has a characteristic thatelectric field concentration in a depletion layer in the vicinity of thedrain region 306 is further effectively relaxed. The concentrationgradient of the Lov region 307 is formed by a method includingaccelerating an n-type or p-type impurity element in an electric fieldand making the impurity element pass through a laminate film of thefirst-layer gate electrode 304 a corresponding to the region that isexposed from the second-layer gate electrode 304 b and the gateinsulating film 303 to be implanted into the island-like semiconductorlayer 302 (through-doping method). The formation of the concentrationgradient arises from the fact that the first-layer gate electrode 304 a(the gate insulating film 303 is irrelevant because it does not changein thickness) which is the upper layer film of the island-likesemiconductor layer 302 becomes thinner toward the end portion inimplanting the impurity to the island-like semiconductor layer 302 withthe through-doping method. Note that, in this specification, a dopingmethod in which an impurity is made to pass through a certain substancelayer positioned as the upper layer of an object substance layer to beimplanted thereto is referred to as “through-doping method” for the sakeof convenience.

Further, in the structure of the GOLD structure TFT having both an Lovregion and an Loff region (FIG. 3B), on a transparent insulatingsubstrate 401, an island-like semiconductor layer 402, a gate insulatingfilm 403, and a gate electrode 404 are laminated from the side closer tothe substrate 401, and a source region 405 and a drain region 406 areformed in the island-like semiconductor layer 402 outside the gateelectrode 404. The above GOLD structure TFT is characterized in that:the gate electrode 404 is constituted of a first-layer gate electrode404 a and a second-layer gate electrode 404 b; the first-layer gateelectrode 404 a is formed longer in size in a channel direction than thesecond-layer gate electrode 404 b; first electric field relaxationregions, that is, Lov regions 407 are formed in the island-likesemiconductor layer 402 corresponding to the regions of the first-layergate electrode 404 a which are exposed from the second-layer gateelectrode 404 b; and second electric field relaxation regions, that is,Loff regions 408 and the source region 405 and the drain region 406 areformed in the island-like semiconductor layer 402 corresponding to theoutside of the gate electrode 404 so as to be adjacent to each otherfrom the side closer to the gate electrode 404.

In the GOLD structure TFT with the above structure, the Lov region 407is the first electric field relaxation region formed so as to overlapwith an end portion of the first-layer gate electrode 404 a, andconsists of an n-type or p-type low concentration impurity region (n⁻⁻region or p⁻⁻ region). The Lov region 407 has a concentration gradientthe impurity concentration of which gradually increases toward the Loffregion 408. Further, the Loff region 408 is the second electric fieldrelaxation region formed so as not to overlap with the first-layer gateelectrode 404 a, and consists of an n-type or p-type low concentrationimpurity region (n⁻ region or p⁻ region). The Loff region 408 has aconcentration gradient the impurity concentration of which graduallyincreases toward the source region 405 or the drain region 406 which isan n-type or p-type high concentration impurity region (n⁺ region or p⁺region). Note that the concentration gradient of the Lov region 407arises from the fact that the first-layer gate electrode 404 a (the gateinsulating film 403 is irrelevant because it does not change inthickness) which is the upper layer film of the island-likesemiconductor layer 402 becomes thinner toward the end portion inimplanting the impurity to the island-like semiconductor layer 402 withthe through-doping method. Similarly, the concentration gradient of theLoff region 408 arises from the fact that the gate insulating film 403that is the upper layer film of the island-like semiconductor layer 402becomes thinner away from the gate electrode 404.

By the way, the gate electrodes 304, 404 of the GOLD structure TFTsshown in FIGS. 3A and 3B are constituted of the first-layer gateelectrodes 304 a, 404 a and the second-layer gate electrodes 304 b, 404b, respectively. The first-layer gate electrodes 304 a, 404 a are formedlonger in size in a channel direction than the second-layer gateelectrodes 304 b, 404 b, respectively. Then, the region of each of thefirst-layer gate electrodes 304 a, 404 a which is exposed from each ofthe second-layer gate electrodes 304 b, 404 b has a thin tapered shape,and thus, has a thinner thickness toward the end portion. A dry etchingmethod that utilizes high density plasma which is capable ofindependently controlling a plasma density and a bias voltage applied toa substrate is suitable for processing of the gate electrodes 304, 404with the above structure. As a specific dry etching method, a dryetching method is known which utilizes a microwave orinductively-coupled-plasma (hereinafter abbreviated to ICP). However,our company employs a dry etching apparatus of an ICP system. This isbecause the ICP dry etching apparatus enables easy control of plasma,and thus, has an advantage that a larger-scale processing substrate canbe easily realized.

In the case where the gate electrodes 304, 404 are processed using theICP dry etching apparatus, it is necessary to perform a dry etchingprocess consisting of a large number of process steps in combination oftaper etching and anisotropic etching. Here, in one process step, anetching process is performed under predetermined etching conditions.Note that the etching conditions mentioned here indicate a chamberpressure, an ICP power density, a bias power density, and a flow ratioof gases constituting etching gas.

For example, in the dry etching step of the gate electrode 304 of theGOLD structure TFT only having an Lov region (see FIG. 3A), the dryetching process consisting of three steps is performed, and thus, achangeover of the etching gas needs to be performed twice. Thechangeover of the etching gas requires a time until the pressure of anetching chamber is stabilized at the time of the changeover, which leadsto the problem of reduction in throughput of the dry etching step.Moreover, there is required the etching gas that is flown until thepressure of the etching chamber is stabilized. Thus, there is also theproblem of rise of the process cost due to consumption amount increaseof the etching gas. Furthermore, in addition to the above problems, thecomplication of the dry etching step leads to the process defect and theincrease of the number of troubles, and also involves the problem ofreduction of yield of a semiconductor device.

Note that the above problems are not limited to the manufacturing stepsof the GOLD structure TFT, and are found in the manufacturing steps ofthe LDD structure TFT as well. This is because the gate electrode isprocessed through the same dry etching step in either the GOLD structureTFT or the LDD structure TFT.

SUMMARY OF THE INVENTION

The present invention has been made in order to solve theabove-mentioned problems in the prior art, and therefore has an objectto provide a semiconductor device manufactured by applying a dry etchingmethod including a small number of process steps for processing of agate electrode and a method of manufacturing the semiconductor device.Note that the semiconductor device in this specification indicatessemiconductor devices in general the circuit of which is configured bysemiconductor devices including a TFT with a GOLD structure. Forexample, semiconductor display devices such as an active matrix liquidcrystal display device and an organic EL display device are included inthe category of the semiconductor device.

[Examination of Reduction of the Number of Process Steps in Dry EtchingStep]

(Structure of ICP Dry Etching Apparatus)

An ICP dry etching apparatus used in this examination will be explainedbelow. The ICP dry etching apparatus adopts a method in which a highfrequency power is applied to a portion consisting of a plurality ofspiral coils through an impedance matching device as a means forconducting a plasma process with high precision to thereby produceplasma. Here, the length of a coil is set to one fourth of a highfrequency wavelength, and also, a high frequency power is independentlyapplied to a lower electrode that holds an object to be processed, tothereby be applied with a bias voltage. Note that the details of the ICPplasma etching apparatus concerned are disclosed in JP 9-293600A.

FIGS. 4A and 4B are schematic diagrams of the ICP dry etching apparatusconcerned. An antenna coil 502 is arranged on a quartz plate 501provided above a reaction space, and is connected to a first highfrequency power source 504 through a matching box 503. The first highfrequency power source 504 supplies a high frequency power of 6 to 60MHz, typically 13.56 MHz. Further, a lower electrode 506 that holds asubstrate 505 as an object to be processed is connected to a second highfrequency power source 508 through a matching box 507. The second highfrequency power source 508 supplies a high frequency power of 100 KHz to60 MHz, for example, 6 to 29 MHz. When the high frequency power isapplied to the antenna coil 502, a high frequency current J flows to theantenna coil 502 in a θ direction, a magnetic field B (Formula 1) isgenerated in a Z direction, and an induction field E (Formula 2) isgenerated in the θ direction in accordance with the law ofelectromagnetic induction of Faraday (see FIG. 4A).

[Formula 1]μ₀ J=rot B$\begin{matrix}{{- \frac{\partial B}{\partial t}} = {{rot}{\quad\quad}E}} & \left\lbrack {{Formula}\quad 2} \right\rbrack\end{matrix}$

Electrons are accelerated in the θ direction to collide with gasmolecules in the induction filed E, thereby producing plasma. Since thedirection of the induction field E is the θ direction, the probabilitythat charged particles collide with an inner wall of a reaction chamberand the substrate 505 to lose energy is small. Further, the magneticfield B hardly affects the portion below the antenna coil 502, and thus,a high density plasma region that is expanded in a flat plate shape isproduced. Then, the high frequency power applied to the lower electrode506 is adjusted, whereby the plasma density and the bias voltage appliedto the substrate 505 can be independently controlled. Further, thefrequency of the high frequency power to be applied can be changed inaccordance with a substance to be etched.

In order to generate high density plasma with the ICP system, the highfrequency current J that flows through the antenna coil needs to beflown at a low loss, and the inductance needs to be lowered. In view ofthis point, a method in which the antenna coil is divided is effective.FIG. 4B is a schematic diagram showing such a structure. A portionconsisting of a plurality of spiral coils 510 is arranged on a quartzsubstrate 509, and is connected to a first high frequency power source512 through a matching box 511. In this case, when the length of onecoil is set to an integral multiple of ¼ of a high frequency wavelength,a standing wave occurs in the coil portion, and a peak value of thegenerated voltage can be increased.

A dry etching step that is a processing step of the gate electrode ofthe GOLD structure TFT is performed by using the ICP dry etchingapparatus with the above structure, but there is a problem in that thedry etching step includes a large number of process steps. Thus, thereduction of the number of process steps is examined.

(Substrate Structure and Etching Gas)

First, the structure of a substrate used in this examination will bedescribed. The substrate used here has a structure in which, on a squareglass substrate (regular square 12.5 cm on a side) such as a Corning1737 substrate, a silicon oxide film with a thickness of 200 nm, a TaNfilm with a thickness of 30 nm, and a W film with a thickness of 370 nmare laminated in order from the side closer to the substrate. Briefly,there is used a substrate with the structure written in the W film(thickness of 370 nm)/TaN film (thickness of 30 nm)/silicon oxide film(thickness of 200 nm)/glass substrate. In the substrate with the abovestructure, a metallic laminate film with a two-layer structureconsisting of the W film (thickness of 370 nm)/TaN film (thickness of 30nm), which is laminated on the silicon oxide film with a thickness of200 nm, corresponds to substances to be etched. Note that, as to theexamination of an etching rate of each film, there is used a substratein which a single layer film comprised of the W film (thickness of 370nm), TaN film (thickness of 30 nm), or silicon oxide film (thickness of200 nm) is deposited on the glass substrate.

By using the substrate with the above structure, the metallic laminatefilm consisting of the W film (thickness of 370 nm)/TaN film (thicknessof 30 nm) is subjected to a dry etching process using a resist patternwith a thickness of 1.5 μm as a mask. In the prior art, the dry etchingprocess consisting of a large number of process steps comprised of taperetching and anisotropic etching is performed, a mixed gas of CF₄, Cl₂,and O₂ is used in the process step of taper etching, and a mixed gas ofSF₆, Cl₂, and O₂ is used in the process step of anisotropic etching. Inthis examination, the etching gas to be used is limited to the mixed gasof SF₆, Cl₂, and O₂, and the examination of the reduction of the numberof process steps is made. Note that, a fluorine-based gas isstandardized to SF₆ from CF₄ in the etching gas comprised of a mixed gasbecause the increase of the etching rate of the W film (thickness of 370nm) and the following improvement of the selection ratio of the W filmto the silicon oxide film (thickness of 200 nm) can be expected byincreasing an existence ratio of a fluoride element.

Note that, hereinafter, description will be made using SF₆ as thegluorine-based gas from the above-mentioned reason, but the presentinvention is not limited to this. SF₆ is the most preferable but otherfluorine-based gas (for example, CF₄) may also be used. Further, aCl-based gas may be used instead of Cl₂.

In this specification, the metallic laminate film is described with thelaminate structure of the combination of the W film and the TaN film,but the present invention is not limited to this. The combination of theW film and the TaN film is the most preferable. However, a metalcompound containing W as a main constituent or WN (tungsten nitride) maybe used instead of W, and Ta may be used instead of TaN.

(Experiment 1)

An evaluation was made on ICP power dependence of an etching rate ofeach of the W film, TaN film, and silicon oxide film using the ICP dryetching apparatus, substrate, and etching gas which are mentioned above.As to the etching conditions except the ICP power, the gas flow rates ofSF₆ and Cl₂, which correspond to the etching gas, are 40 sccm and 20sccm, respectively (In this case, the gas flow rate of O₂ is 0 sccm.),the chamber pressure is 1.3 Pa, and the bias power is 20 W (bias powerdensity: 0.128 W/cm²). Under the above conditions, an experiment wasmade with respect to 500 W (ICP power density: 1.019 W/cm²), 700 W (ICPpower density: 1.427 W/cm²), and 900 W (ICP power density: 1.834 W/cm²)in ICP power. Note that the bias power indicates the power applied tothe substrate 505 from the second high frequency power source 508, andthe bias power density indicates a value obtained by dividing the biaspower by the area of the substrate 505 (regular square 12.5 cm on aside). Further, the ICP power indicates the power applied to the portionconsisting of a plurality of spiral coils 510 from the first highfrequency power source 512, and the ICP power density indicates a valueobtained by dividing the ICP power by the area of the portion consistingof a plurality of spiral coils 510 (circular region with a diameter of25 cm) (see FIGS. 4A and 4B).

The results of this experiment are shown in FIGS. 5A and 5B. Asunderstood from FIG. 5A, it was found that, along with the increase ofthe ICP power, while the etching rates of the TaN film and the siliconoxide film were hardly increased, the etching rate of the W film wasincreased. FIG. 5B shows the results of the evaluation of the selectionratios of the W film to the TaN film and to the silicon oxide film basedon the results of the etching rates. As understood from FIG. 5B, therise of the selection ratio of the W film to the TaN film and the riseof the selection ratio of the W film to the silicon oxide film are founddue to the increase of the ICP power. From the results of thisexperiment, it is found that the increase of the ICP power is preferablefrom the viewpoint of the etching rate and the selection ratio of the Wfilm. However, the ICP power of the dry etching apparatus has themaximum value of 1 kW, and a load applied to the dry etching apparatusis concerned when the apparatus is used with the ICP power of about 1kW. Therefore, the results of this experiment and the load applied tothe dry etching apparatus are compared and considered, and as a result,it is judged that an ICP power of about 700 W is suitable.

(Experiment 2)

Next, in the state in which the gas flow rates of SF₆ and Cl₂ whichcorrespond to the etching gas and the total gas flow rate are fixed toSF₆: Cl₂=2:1 and 60 sccm, respectively, an evaluation is made on theoxygen addition amount dependence of the respective etching rates of theW film, the TaN film, and the silicon oxide film with the additionamount of oxygen (O₂) gas being changed from 0 to 60%. As to the etchingconditions except the gas flow rate, the chamber pressure is 1.3 Pa, andthe bias power is 10 W (bias power density: 0.064 W/cm²). Then, underthe condition of the ICP power of 500 W (ICP power density: 1.019W/cm²), the evaluation of the etching rates was made with the oxygenaddition amount being changed to 20, 40, and 60%. At the same time, anevaluation is made on the case where the ICP power is 700 W (ICP powerdensity: 1.427 W/cm²) and the oxygen addition amount is 40%. Note thatTable 1 shows the details of the dry etching conditions of thisexperiment for reference. TABLE 1 Oxygen Gas flow ICP Bias addition rate(sccm) Pressure power power amount (%) SF₆ Cl₂ O₂ (Pa) (W) (W)  0 40 20 0 1.3 500 10 20 32 16 12 1.3 500 10 40 24 12 24 1.3 500 10 60 16  8 361.3 500 10 40 24 12 24 1.3 700 10

FIGS. 6A and 6B show results of this experiment. As understood from FIG.6A, it is found that, in the case of an ICP power of 500 W, the etchingrate of the W film becomes maximum when the oxygen addition amount is40%. On the other hand, there is found a tendency that the etching rateof the TaN film lowers along with the increase of the oxygen additionamount. Further, as to the etching rate of the silicon oxide film, thereis found no particular tendency except the point that the etching ratelowers when the oxygen addition amount is 0%. FIG. 6B shows the resultof the evaluation of the selection ratios of the W film to the TaN filmand to the silicon oxide film based on the results of the etching rates.As understood from FIG. 6B, there is found a tendency that the selectionratio of the W film to the TaN film increases along with the increase ofthe oxygen addition amount. Further, there is found a tendency that theselection ratio of the W film to the silicon oxide film contrary lowers.It is considered that an ICP power of about 700 W is suitable from theresults of FIGS. 5A and 5B, and that the oxygen addition amount of 40%is the most suitable from the results of this experiment (FIGS. 6A and6B). Thus, the etching rate and the selection ratio are similarlyevaluated with respect to the case of the ICP power of 700 W and theoxygen addition amount of 40%, and the results are shown in the rightends of FIGS. 6A and 6B. From the results concerned, under the etchingconditions of: respective gas flow rates of SF₆, Cl₂, and O₂ as etchinggas of 24, 12, and 24 sccm (corresponding to the oxygen addition amountof 40%), a chamber pressure of 1.3 Pa, an ICP power of 700 W, and a biaspower of 10 W, the etching rate of the W film of 227 nm, the etchingrate of the TaN film of 32 nm, and the etching rate of the silicon oxidefilm of 34 nm can be obtained, and the selection ratio of the W film tothe TaN film of 7.1 and the selection ratio of the W film to the siliconoxide film of 6.8 can be obtained.

(Experiment 3)

Dry etching conditions are set to the following conditions in Table 2.Then, a substrate with the structure consisting of a W film (thicknessof 370 nm)/silicon oxide film (thickness of 200 nm)/glass substrate anda substrate with the structure consisting of a W film (thickness of 370nm)/TaN film (thickness of 30 nm)/silicon oxide film (thickness of 200nm)/glass substrate are each subjected to a dry etching process using aresist pattern with a thickness of 1.5 μm as a mask. TABLE 2 Flow ratesof etching gases SF₆: 24 sccm Cl₂: 12 sccm O₂: 24 sccm Chamber pressure1.3 Pa ICP power 700 W ICP power density 1.427 W/cm² Bias power 10 WBias power density 0.064 W/cm²

FIG. 7A shows an SEM photograph in the case where the dry etchingprocess is performed to the substrate with the structure consisting of aW film (thickness of 370 nm)/silicon oxide film (thickness of 200nm)/glass substrate, and also in the case where over etching isperformed from the end point of etching of the W film for about 20seconds. As understood from FIG. 7A, it is found that the W film hasundergone side etching by about 0.2 to 0.3 μm in the state in which thesilicon oxide film, which is a base film of the W film, is exposed.Further, FIG. 7B shows an SEM photograph in the case where the dryetching process is performed to the substrate with the structureconsisting of a W film (thickness of 370 nm)/TaN film (thickness of 30nm)/silicon oxide film (thickness of 200 nm)/glass substrate, and alsoin the case where over etching is performed from the end point ofetching of the-W film for about 30 seconds. As understood from FIG. 7B,it is not found that the W film has undergone side etching in the statein which the TaN film, which is a base film of the W film, is exposed.From the above, it is understood that there is a causal relationshipbetween side etching of the W film and the exposure of the silicon oxidefilm in over etching. In the case where the silicon oxide film isexposed in over etching, oxygen emission from the silicon oxide film isconsidered, and the existence of the emitted oxygen is considered to bea direct cause of side etching of the W film. Taking this point intoconsideration, the dry etching process is performed to the substratewith the structure consisting of a W film (thickness of 370 nm)/TaN film(thickness of 30 nm)/silicon oxide film (thickness of 200 nm)/glasssubstrate, and over etching is performed from the end point of etchingof the TaN film for a predetermined time. As a result, as shown in anSEM photograph of FIG. 7C, an etching shape with side etching of about0.2 to 0.3 μm can be obtained in the W film in the state in which thesilicon oxide film, which is the base film of the TaN film, is exposed.Further, it is confirmed that the region of the TaN film which isexposed from the W film gradually becomes thinner toward the endportion.

(Construction of Process Step Reduction Process)

It is considered that a metal laminate pattern consisting of the Wfilm/TaN film in which the W film has undergone side etching, which isshown in the SEM photograph of FIG. 7C, can be applied to the gateelectrode of the GOLD structure TFT (also including the LDD structureTFT). This is because the gate electrode of the GOLD structure TFT (alsoincluding the LDD structure TFT) developed by our company ischaracterized in that: it is constituted of the TaN film as thefirst-layer gate electrode and the W film as the second-layer gateelectrode; the first-layer gate electrode (TaN film) is larger inchannel direction size than the second-layer gate electrode (W film);and the region of the first-layer gate electrode which is exposed fromthe second-layer gate electrode becomes thinner toward the end portion,and because the gate electrode has substantially the same shape as themetal laminate pattern in FIG. 7C. Therefore, it is considered that thegate electrode of the GOLD structure TFT (also including the LDDstructure TFT) can be formed by a one-step dry etching process under thedry etching conditions for a one-step process in Table 2. The substratesectional views showing the dry etching process in this case are shownin FIGS. 1A and 1B.

Here, the one-step dry etching process indicates that an etching processis conducted once under predetermined etching conditions, and theetching conditions indicate a chamber pressure, an ICP power density, abias power density, and a flow rate of respective gases constitutingetching gas. Further, the dry etching conditions for the one-stepprocess in Table 2 show preferable values, and thus, the presentinvention is not limited to these values.

The substrate sectional view of FIG. 1A shows the first half of theone-step dry etching process, in which a second-layer gate electrode 105comprised of a W film and a first-layer gate electrode 106 comprised ofa TaN film are subjected to anisotropic etching with a resist pattern104 as a mask. In this case, the resist pattern 104 is slightlyretreated from end portions of the initial resist pattern due toetching, a gate insulating film 103 that is a base silicon oxide film isexposed, and the reduction in thickness progresses in the region outsidethe end portions of the initial resist pattern. Note that the gateinsulating film 103 corresponding to the region inside the end portionof the initial resist pattern is formed into a tapered shape along withthe-retreat of the end portion of the resist pattern 104 due to etching,and becomes thinner away from an end portion of the first-layer gateelectrode 106. Further, FIG. 1B shows a substrate sectional view in thelatter half of the dry etching process, in which reduction in thicknessof the silicon oxide film that is a base gate insulating film 109 isfurther progressed as a whole, and side etching of the W film that is asecond-layer gate electrode 107 is progressed with an influence ofoxygen emitted from the silicon oxide film. In this case, the region ofa first-layer gate electrode 108 which is exposed from the second-layergate electrode 107 is etched into a tapered shape, and becomes thinnertoward the end portion. Further, the gate insulating film 109corresponding to the region inside the end portion of the initial resistpattern is entirely thinned while maintaining the same tapered shape asthat in the first half step of the dry etching process.

Note that the silicon oxide film is used as the gate insulating filmhere, and is the most preferable one. However, the present invention isnot limited to this. As described above, it is considered that thesilicon oxide film is exposed in over etching, and that oxygen emittedfrom the silicon oxide film causes side etching of the W film.Therefore, it is considered that the same effect can be obtained with afilm other than the silicon oxide film as long as the film is an oxidefilm.

Further, it is expected that side etching of the W film, which is thesecond-layer gate electrode, can be promoted without exposure of thebase silicon oxide film by increasing the oxygen addition amount basedon the findings of the dry etching conditions of the above one-stepprocess. Thus, the dry etching process was performed for a predeterminedtime under the dry etching conditions in which the oxygen additionamount is increased from 24 sccm to 30 sccm. FIG. 2A is a sectional viewshowing a substrate after the dry etching process, in which isotropicetching can be performed to a W film that is a second-layer gateelectrode 205 a in the state in which a TaN film 206 remains. In thiscase, an end portion of the resist pattern 204 a is retreated from theinitial resist pattern end portion due to etching, whereby etchingproceeds in the TaN film 206 such that the region inside the initialresist pattern end portion has a tapered shape. The TaN film 206 becomesthinner away from an end portion of the second-layer gate electrode (Wfilm) 205 a, and thus, has a given residual film thickness in the regionoutside the initial resist pattern end portion. FIG. 2B is a substratesectional view after the dry etching process for a predetermined timeunder the dry etching conditions of a gas flow rate of Cl₂, which isetching gas, of 60 sccm, a chamber pressure of 1.0 Pa, an ICP power of350 W (ICP power density: 0.713 W/cm²), and a bias power of 20 W (biaspower density: 0.128 W/cm²), which is performed for anisotropic etchingto the TaN film 206. At this time, a first-layer gate electrode 207formed through anisotropic etching of the TaN film 206 gradually becomesthinner away from an end portion of a second-layer gate electrode (Wfilm) 205 b, and suddenly comes to the end at an end portion thereof dueto the combination of taper etching and anisotropic etching. Further,etching proceeds in a gate insulating film 208 comprised of a siliconoxide film such that the region inside the initial resist pattern endportion has a tapered shape. The gate insulating film 208 becomesthinner away from the end portion of the first-layer gate electrode 207,and thus, has a given residual film thickness in the region outside theinitial resist pattern end portion (refer to FIG. 2B).

From the above results, it is considered that the two-step dry etchingprocess conditions can be applied to the dry etching step of the gateelectrode of the GOLD structure TFT (also including the LDD structureTFT). The details of the two-step dry etching process conditions aredescribed in Table 3.

Here, the two-step dry etching process indicates that a dry etchingprocess for the first step is performed under predetermined etchingconditions, and a dry etching process for the second step is performedunder predetermined etching conditions different from those in the firststep. Note that the two-step dry etching process conditions in Table 3show preferable values, but the present invention is not limited tothese values. TABLE 3 (1) 1st step Flow rates of etching gases SF₆: 24sccm Cl₂: 12 sccm O₂: 30 sccm Chamber pressure 1.3 Pa ICP power 700 WICP power density 1.427 W/cm² Bias power 10 W Bias power density 0.064W/cm²2 (2) 2nd step Flow rate of etching gas Cl₂: 60 sccm Chamberpressure 1.0 Pa ICP power 350 W ICP power density 0.713 W/cm² Bias power20 W Bias power density 0.128 W/cm²

From the above results, the substrate with the structure consisting of aW film (thickness of 370 nm)/TaN film (thickness of 30 nm)/silicon oxidefilm (thickness of 200 nm)/glass substrate is subjected to the dryetching process under the one-step dry etching process conditions (seeTable 2) or the two-step dry etching process conditions (see Table 3),whereby the gate electrode of the GOLD structure TFT (also including theLDD structure TFT) can be processed. Therefore, the dry etching processis performed under the one-step dry etching process conditions or thetwo-step dry etching process conditions, whereby it is considered thatthe problems in the prior art in the processing step of the gateelectrode of the GOLD structure TFT (also including the LDD structureTFT) can be solved.

[Semiconductor Device and Method of Manufacturing the Same]

Description will be made of the structure of the invention relating to asemiconductor device and a method of manufacturing the same in the casewhere the dry etching process consisting of one step or two steps isapplied to the dry etching process of the gate electrode of the GOLDstructure TFT (also including the LDD structure TFT).

(Structure of the Invention relating to Semiconductor Device)

The structure of the present invention relating to the semiconductordevice relates to the semiconductor device the circuit of which isconfigured by a plurality of TFTs including a GOLD structure TFT formedon a principal surface of a transparent insulating substrate, the GOLDstructure TFT being such that: a semiconductor layer, a gate insulatingfilm, and a gate electrode are formed in lamination from the side closerto the transparent insulating substrate; the gate electrode isconstituted of a first-layer gate electrode and a second-layer gateelectrode that is shorter in size in a channel direction than thefirst-layer gate electrode; the first-layer gate electrode correspondingto the region exposed from the second-layer gate electrode is formedinto a tapered shape so as to gradually become thinner toward the endportion thereof; a first impurity region having one conductivity isformed in the semiconductor layer corresponding to the region of thefirst-layer gate electrode which is exposed from the second-layer gateelectrode; and a second impurity region having the same conductivity asthe first impurity region is formed in the semiconductor layercorresponding to the outside of the first-layer gate electrode, which ischaracterized in that: a dry etching process consisting of one step ortwo steps is applied to the formation of the gate electrode; thesecond-layer gate electrode is formed by isotropic etching through thedry etching process; and the first-layer gate electrode corresponding tothe region exposed from the second-layer gate electrode is formed bytaper etching through the dry etching process.

In the structure of the above invention, the transparent insulatingsubstrate may be any one as long as it is a transparent substrate havinginsulating property. For example, a glass substrate or a quartzsubstrate may be used. Further, the semiconductor layer indicates anisland-like semiconductor layer functioning as an active layer of a TFT,and includes a polycrystalline silicon film having semiconductorcharacteristics or a crystalline silicon film formed throughcrystallization by utilizing a catalytic element. The thickness range ofthe polycrystalline silicon film or crystalline silicon film is suitablyabout 20 to 200 nm, more preferably about 30 to 70 nm. Note that, inthis specification, the polycrystalline silicon film formed by utilizinga catalytic element is referred to as a crystalline silicon film inorder to distinguish it from a general polycrystalline silicon film.Here, the reason why “crystalline” is used for the silicon film insteadof “polycrystalline” is that since the crystalline silicon film hascharacteristics that the crystal grains are orientated in substantiallythe same direction and that it has a high field-effect mobility incomparison with the general polycrystalline silicone film, thecrystalline silicon film is distinguished from the generalpolycrystalline silicon film.

Further, in the structure of the above invention, the gate insulatingfilm is comprised of a silicon oxide film or a silicon oxynitride film,and has a tapered shape so as to be thinner away from the end portion ofthe gate electrode at a given distance from the end portion of the gateelectrode. Note that the thickness of the gate insulating film at thefilm deposition is suitably about 30 to 200 nm, more preferably about 80to 130 nm. The reason why the thickness of about 80 to 130 nm ispreferable is that a thickness of 80 nm or more is required in order toprevent electrical characteristics of a TFT from being affected due to astress from the upper layer gate electrode (laminate gate electrode of Wfilm/TaN film).

Further, in the structure of the above invention, the gate electrode isconstituted of the first-layer gate electrode comprised of a TaN filmwith a thickness of about 5 to 50 nm, preferably about 20 to 40 nm andthe second-layer gate electrode comprised of a W film with a thicknessof about 200 to 600 nm, preferably about 300 to 500 nm, more preferablyabout 350 to 500 nm. The first-layer gate electrode corresponding to theregion exposed from the second-layer gate electrode is formed into atapered shape so as to gradually become thinner toward the end portionthereof. Note that the thickness range of the TaN film is determined inaccordance with a good balance between controllability of the thicknessin the tapered shape region in dry etching and implantationcharacteristics in implantation of an impurity element through the TaNfilm with a through-doping method. Further, the thickness range of the Wfilm is determined by a good balance between prevention of a channelingphenomenon of the W film in implantation of an impurity element andelectric resistance of the W film. The channeling phenomenon is aphenomenon in which part of implantation ions enter the semiconductorlayer in the lower portion without colliding with W atoms. It is knownthat a thickness of at least 340 nm or more is required in order toprevent the channeling phenomenon.

Further, in the structure of the above invention, the first impurityregion indicates a low concentration impurity region having n-type orp-type conductivity (n⁻ region, p⁻ region), and functions as an electricfield relaxation region for relaxing an electric field in a channelhorizontal direction. Further, the second impurity region indicates ahigh concentration impurity region having the same conductivity as thefirst impurity region (n⁺ region, p⁺ region), and functions as a sourceregion or a drain region. Note that the first impurity region has aconcentration gradient the impurity concentration of which graduallyincreases away from an end portion of the second-layer gate electrode.Further, the second impurity region has a concentration gradient in aregion at a given distance from the end portion of the first-layer gateelectrode, and the impurity concentration gradually increases away fromthe end portion of the first-layer gate electrode.

According to the invention structured as described above, the gateelectrode of the semiconductor device the circuit of which is configuredby a plurality of TFTs including the GOLD structure TFT can be processedby the dry etching process consisting of one step or two steps.Accordingly, there can be solved the problems in the prior art in thedry etching process, that is, reduction in throughput of the dry etchingprocess, rise of the process cost that follows consumption amountincrease of etching gas, and further, reduction of yield of asemiconductor device which follows complication of the dry etchingprocess.

(Structure of the Invention relating to Method of ManufacturingSemiconductor Device)

The structure of the present invention relating to a method ofmanufacturing a semiconductor device relates to a method ofmanufacturing a semiconductor device, including: a first step of forminga semiconductor layer on a principal surface of a transparent insulatingsubstrate; a second step of depositing a gate insulating film to coverthe semiconductor layer; a third step of depositing a first-layer gateelectrode film on the gate insulating film; a fourth step of depositinga second-layer gate electrode film on the first-layer gate electrodefilm; a fifth step of forming a resist pattern for formation of a gateelectrode; a sixth step of performing a dry etching process to alaminate film constituted of the first-layer gate electrode film and thesecond-layer gate electrode film to form a gate electrode constituted ofa first-layer gate electrode and a second-layer gate electrode shorterin size in a channel direction than the first-layer gate electrode withthe resist pattern as a mask; a seventh step of removing the resistpattern; and an eighth step of forming a first impurity region in thesemiconductor layer corresponding to the region of the first-layer gateelectrode which is exposed from the second-layer gate electrode and atthe same time, forming a second impurity region in the semiconductorlayer corresponding to the outside of the first-layer gate electrode byimplantation of an impurity element having one conductivity, which ischaracterized in that: the gate electrode is formed by a dry etchingprocess consisting one step or two steps; the second-layer gateelectrode is formed by isotropic etching through the dry etchingprocess; and the first-layer gate electrode corresponding to the regionexposed from the second-layer gate electrode is formed by taper etchingthrough the dry etching process.

In the structure of the above invention, the transparent insulatingsubstrate may be any one as long as it is a transparent substrate havinginsulating property. For example, a glass substrate or a quartzsubstrate may be used. Further, the semiconductor layer is anisland-like semiconductor layer that functions as an active layer of aTFT, and is comprised of a polycrystalline silicon film or a crystallinesilicon film (silicon semiconductor film crystallized by utilizing acatalytic element) having semiconductor characteristics with a thicknessof about 20 to 200 nm, preferably about 30 to 70 nm. Further, either asilicon oxide film or a silicon oxynitride film may be applied to thegate insulating film, and the thickness range is suitably about 30 to200 nm, more preferably about 80 to 130 nm. Further, a TaN film with athickness of about 5 to 50 nm, preferably about 20 to 40 nm is appliedto the first-layer gate electrode film, and a W film with a thickness ofabout 200 to 600 nm, preferably about 300 to 500 nm, more preferablyabout 350 to 500 nm is applied to the second-layer gate electrode film.

Further, in the structure of the above invention, a metallic laminatefilm constituted of the first-layer gate electrode film and thesecond-layer gate electrode film is subjected to a dry etching processconsisting of one step or two steps with the resist pattern as a mask,thereby forming the gate electrode. In this case, since the second-layergate electrode is formed by isotropic dry etching, the second-layer gateelectrode is shorter in size in a channel direction than the fist-layergate electrode. Further, the first-layer gate electrode corresponding tothe region exposed from the second-layer gate electrode is formed into atapered shape so as to be gradually thinner toward the end portion bytaper etching. Further, a dry etching method with the use of highdensity plasma, which is capable of independently controlling a plasmadensity and a bias voltage applied to a subject substrate, isappropriate for the dry etching process, and for example, an ICP dryetching apparatus is suitable.

Specific dry etching conditions of the ICP dry etching apparatus are thedry etching conditions described in Tables 2 and 3 as standards. The dryetching conditions in Tables 2 and 3 correspond to a square substrate12.5 cm on a side. It is considered that, in the case of the actuallarge-scale square substrate, for example, a large-scale substrate about1 m on a side, a gas flow rate of etching gas greatly differs along withthe increase of the volume in an etching chamber. Therefore, aregulation needs to be placed on not a gas flow rate but a gas flowratio in order to provide the dry etching conditions with versatility.Further, it is considered that respective parameters in the dry etchingconditions slightly change when a different apparatus is used even if itis the same model ICP dry etching apparatus. Moreover, the dry etchingconditions need to be regulated in consideration of a degree of room inprocess in the dry etching process. In view of the above points, anumerical range needs to be introduced for each parameter in the dryetching conditions, and Tables 4 and 5 show the dry etching conditionsin which the numerical range is introduced for each parameter. Here,Table 4 corresponds to the dry etching conditions adapted for a one-stepprocess, and Table 5 corresponds to the dry etching conditions adaptedfor a two-step process. An etching process may be performed with apredetermined value in the numerical range shown in Table 4 or Table 5.Note that, in Tables 4 and 5, parameters of a gas flow ratio, an ICPpower density, and a bias power density are regulated with the purposeof avoiding the influence of a substrate size of a subject substrate.TABLE 4 Gas flow rate SF₆/Cl₂/O₂ = 2/1/2 Chamber pressure 1.0˜1.6 Pa ICPpower density 1.02˜2.04 W/cm² Bias power density 0.03˜0.19 W/cm²

TABLE 5 1st step process Gas flow rate SF₆/Cl₂/O₂ = 4/2/5 Chamberpressure 1.0˜1.6 Pa ICP power density 1.02˜2.04 W/cm² Bias power density0.03˜0.19 W/cm² 2nd step process Gas: Cl₂ SF₆/Cl₂/O₂ = 0/1/0 Chamberpressure 0.8˜1.2 Pa ICP power density 0.51˜1.02 W/cm² Bias power density0.03˜0.32 W/cm²

Further, in the structure of the above invention, as to the impurityelement having one conductivity, an n-type impurity typified by aphosphorous element may be implanted, or a p-type impurity typified by aboron element may be implanted. Through implantation of the aboveimpurity elements, the first impurity region is formed in thesemiconductor layer corresponding to the region of the first-layer gateelectrode which is exposed from the second-layer gate electrode by athrough-doping method, and at the same time, the second impurity regionis formed in the semiconductor layer corresponding to the outside of thefirst-layer gate electrode by the through-doping method. At this time,since the impurity regions are simultaneously formed by thethrough-doping method, the impurity concentrations of the first impurityregion and the second impurity region are determined depending on anacceleration voltage and a dosage at the time of implantation of theimpurity elements and further on the kind and thickness of the upperlayer film of each of the impurity regions. For example, in the firstimpurity region, the first-layer gate electrode constituted of the gateinsulating film and the TaN film exists as the upper layer film, an ionblocking ability of the upper layer film is large, and thus, a lowconcentration impurity region (n⁻ region, p⁻ region) having n-type orp-type conductivity is formed. In this case, since the first-layer gateelectrode comprised of the TaN film, which is a part of the upper layerfilm, is formed into a tapered shape by taper etching, the firstimpurity region is imparted with a concentration gradient the impurityconcentration of which gradually increases toward the second impurityregion. On the other hand, in the second impurity region, only the gateinsulating film exists as the upper layer film, the ion blocking abilityof the upper layer film is not so large, and thus, a high concentrationimpurity region (n⁺ region, p⁺ region) having n-type or p-typeconductivity is formed. In this case as well, since a tapered shaperegion exists in a specific region of the gate insulating film that isthe upper layer film, the second impurity region is imparted with aconcentration gradient in a region at a given distance from the endportion of the first-layer gate electrode. Note that the first impurityregion has a function as an electric field relaxation region forrelaxing an electric field in a channel horizontal direction, and thesecond impurity region is formed so as to have a function of a sourceregion or a drain region.

According to the present invention structured as described above, thegate electrode of the semiconductor device the circuit of which isconfigured by a plurality of TFTs including the GOLD structure TFT canbe processed by the dry etching process consisting of one step or twosteps. Accordingly, there can be solved the problems in the prior art inthe dry etching process, that is, reduction in throughput of the dryetching process, rise of the process cost that follows consumptionamount increase of etching gas, and further, reduction of yield of asemiconductor device which follows complication of the dry etchingprocess.

By the way, the structure of the present invention is similar to thedisclosed technique in JP 7-202210A described as a known example, butthe structure of the invention differs between both the sides in thefollowing basic points. In the disclosed technique in JP 7-202210A, anexample of wet etching or a combination of anode oxidization and wetetching is described in a step of forming a second gate electrodeshorter in the dimension in a channel direction than a first-layer gateelectrode. In this case, in the formation step of the second-layer gateelectrode, the region of the first-layer gate electrode which is exposedfrom the second-layer gate electrode is hardly reduced in thickness, andthus, the formation of the first-layer gate electrode having arectangular shape is expected. Also, in the sectional view showing amanufacturing step, the rectangular first-layer gate electrode is shown.On the contrary, the structure of the present invention is characterizedin that a first-layer gate electrode corresponding to the region exposedfrom a second-layer gate electrode is formed into a tapered shape so asto be gradually thinner toward the end portion thereof. Thus, a firstimpurity region that is an electric field relaxation region is impartedwith a concentration gradient in implanting an impurity element by athrough-doping method. The concentration gradient promotes an electricfield relaxing effect of the first impurity region, and is extremelyeffective in preventing a hot carrier phenomenon. Accordingly, it isconsidered that matters for invention specification essentially differbetween the present invention and the known example.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B are substrate sectional views showing a one-step dryetching process;

FIGS. 2A and 2B are substrate sectional views showing a two-step dryetching process;

FIGS. 3A and 3B show examples of sectional views each showing a GOLDstructure TFT developed by our company;

FIGS. 4A and 4B are schematic diagrams of an ICP dry etching apparatus;

FIGS. 5A and 5B are diagrams showing ICP power dependence of an etchingrate and of a selection ratio;

FIGS. 6A and 6B are diagrams showing oxygen addition amount dependenceof an etching rate and of a selection ratio;

FIGS. 7A to 7C show SEM photographs of the state obtained after a dryetching process;

FIGS. 8A to 8D are sectional views showing manufacturing steps of asemiconductor display device having an LDD structure TFT and a GOLDstructure TFT;

FIGS. 9A and 9B are sectional views showing manufacturing steps of asemiconductor display device having an LDD structure TFT and a GOLDstructure TFT;

FIGS. 10A and 10B are a partial enlarged view of a step sectional viewof a GOLD structure TFT, and a conceptual diagram showing a distributionof an impurity concentration in a semiconductor layer, respectively;

FIGS. 11A to 11D are sectional views showing manufacturing steps of asemiconductor display device having an LDD structure TFT and a GOLDstructure TFT;

FIGS. 12A to 12D are sectional views showing manufacturing steps of asemiconductor display device having an LDD structure TFT and a GOLDstructure TFT;

FIGS. 13A and 13B are sectional views showing manufacturing steps of anactive matrix liquid crystal display device;

FIGS. 14A and 14B are sectional views showing manufacturing steps of anactive matrix liquid crystal display device;

FIGS. 15A and 15B are sectional views showing manufacturing steps of anactive matrix liquid crystal display device;

FIGS. 16A and 16B are sectional views showing manufacturing steps of anactive matrix liquid crystal display device;

FIGS. 17A and 17B are sectional views showing manufacturing steps of anactive matrix liquid crystal display device;

FIGS. 18A and 18B are sectional views showing manufacturing steps of anactive matrix liquid crystal display device;

FIGS. 19A to 19F are schematic diagrams showing examples of electronicdevices each of which is incorporated with a semiconductor displaydevice;

FIGS. 20A to 20D are schematic diagrams showing examples of electronicdevices each of which is incorporated with a semiconductor displaydevice; and

FIGS. 21A to 21C are schematic diagrams showing examples of electronicdevices each of which is incorporated with a semiconductor displaydevice.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiment modes of the present invention will bespecifically described-with reference to FIGS. 8A to 12D. Here, FIGS. 8Ato 9B and FIGS. 11A to 12D are sectional views for showing manufacturingsteps in accordance with the embodiment modes of the present invention.FIG. 10B is a conceptual view for showing an impurity concentrationdistribution of a semiconductor layer.

EMBODIMENT MODE 1

In this embodiment mode, a description will be given of manufacturingsteps of a semiconductor display device having TFTs of an LDD structureand a GOLD structure on a glass substrate as a transparent insulatingsubstrate with reference to FIGS. 8A to 10B. Note that, a specificcircuit configuration is as follows: a pixel TFT is composed using anLDD structure excellent in low OFF current characteristics and ann-channel or a p-channel driver circuit is composed using a GOLDstructure high in resistance to hot carriers.

First, on a glass substrate 601 as a transparent insulating substratewhich is formed in a square shape with a side being 12.5 cm, anamorphous silicon film having a thickness of 20 to 200 nm, preferably 30to 70 nm, is deposited by a plasma CVD method or a reduced pressure CVDmethod. In this embodiment mode, the amorphous silicon film having athickness of 53 nm is deposited. Thereafter, a polycrystalline siliconfilm is formed with a thickness of 50 nm through heat treatment. At thistime, examples of a heat-treatment method for the amorphous silicon filmmay include heat treatment at 600° C. for about 24 hours using furnaceannealing and laser crystallization at a laser power density of 200mJ/cm² or more, and a combination of heat treatment using furnaceannealing and laser crystallization. Note that, in this embodiment mode,the polycrystalline silicon film is adapted thereto, but a crystallinesilicon film may be adapted thereto, which is subjected to thermalcrystallization through addition of a catalytic element having an actionof promoting crystallization. Also, after the polycrystalline siliconfilm or the crystalline silicon film is formed, a channel doping stepmay be performed in order to control a threshold voltage of the TFT insome cases. The channel doping step concerned is performed using amethod of implanting a p-type impurity (specifically, a boron element)into an entire substrate surface at a small dosage in order to make ann-channel TFT an enhancement type (see FIG. 8A).

Next, generally used photolithography and dry etching processes arepreformed to form an island-like semiconductor layer 602 throughpatterning with a predetermined pattern shape and a predetermined size.After pattern formation, a silicon oxide film or a silicon oxynitridefilm is deposited as a gate insulating film 603 a with a thickness of 30to 200 nm, preferably 80 to 130 nm by a plasma CVD method or a reducedpressure CVD method so as to cover the semiconductor layer 602. In thisembodiment mode, the gate insulating film 603 a made of a silicon oxidefilm having a thickness of 100 nm is deposited by a plasma CVD method.Note that, it is known that the gate insulating film 603 a is requiredto have a thickness of 80 nm or more to avoid a stress applied from agate electrode (gate electrode made of lamination of a W film and a TaNfilm) located in an upper layer. Thus, it is determined while takinginto account this point (see FIG. 8A).

Next, a first-layer gate electrode film 604 a made of a TaN film havinga thickness of 5 to 50 nm, preferably 20 to 40 nm, is deposited by asputtering method. In this embodiment mode, the first-layer gateelectrode film 604 a made of a TaN film having a thickness of 30 nm isdeposited. Thereafter, a second-layer gate electrode film 605 a made ofa W film having a thickness of 200 to 600 nm, preferably 300 to 500 nm,more preferably 350 to 500 nm is deposited by a sputtering method. Inthis embodiment mode, the second-layer gate electrode film 605 a made ofa W film having a thickness of 370 nm is deposited. Note that, thethickness of the TaN film is determined while considering both ofcontrollability of a residual film thickness in a taper-shaped regionupon dry etching and implantation characteristics upon implantation ofan impurity element through the TaN film by a through-doping method.Further, it is known that the W film is required to have a thickness of340 nm or more in order to prevent channeling phenomenon from occurringin the W film upon the implantation of the impurity element. Thus, it isdetermined while taking into account this point. In this way, a metalliclaminate film having a two-layer structure is deposited, followed by thegeneral photolithography process. Thus, a resist pattern 606 a forforming a gate electrode is formed (see FIG. 8A).

Next, a metallic laminate film is subjected to a dry etching processusing the resist pattern 606 a as a mask, the film including thefirst-layer gate electrode film 604 a made of a TaN film with athickness of 30 nm and the second-layer gate electrode film 605 a madeof a W film with a thickness of 370 nm. At this time, a dry etching stepof one-step process or two-step process is adapted thereto, so that agate electrode consisting of the first-layer gate electrode 604 b andthe second-layer gate electrode 605 b is formed. In the dry etchingprocess concerned, since the second-layer gate electrode 605 b is formedby isotropic etching, the second-layer gate electrode 605 b is decreasedin size in a channel direction compared with the first-layer gateelectrode 604 b. Also, portions of the first-layer gate electrode 604 bcorresponding to exposed regions that protrude from the second-layergate electrode 605 b are formed by taper etching of the dry etchingprocess concerned, and thus are formed into a tapered shape while beinggradually thinned toward end portions. Also, the gate insulating film603 b is subjected to etching in regions at a given distance from theend portions of the first-layer gate electrode 604 b due to filmreduction in dry etching and is formed into a tapered shape. As thedistance from the first-layer gate electrode 604 b increases, the filmbecomes thinner and further, a residual film thickness is maintained asa thickness outside the above regions at the given distance. Inaddition, after development, the resist pattern 606 a is changed into aresist pattern 606 b in shape due to film reduction in dry etching (seeFIG. 8B).

Here, for the above dry etching process, a dry etching method utilizinghigh density plasma which can independently control plasma density and abias voltage applied to a subject substrate is suitable. Our companyemploys an ICP dry etching apparatus. Specific conditions of dry etchingin the ICP dry etching apparatus concerned are as follows. That is,although differing between the dry etching step of one-step process andthat of two-step process, the conditions employ dry etching conditionsshown in Table 2 in the case of one-step process and employ those shownin Table 3 in the case of two-step process. In other words, in the caseof dry etching step of one-step process, processing is performed underthe etching conditions of the respective gas flow rates of SF₆, Cl₂, andO₂ as etching gas of 24 sccm, 12 sccm, and 24 sccm (corresponding to theoxygen addition amount of 40%), a chamber pressure of 1.3 Pa, an ICPpower of 700 W (ICP power density: 1.427 W/cm²), and a bias power of 10W (bias power density: 0.064 W/cm²). On the other hand, in the case ofdry etching step of two-step process, processing of a first step isperformed under the dry etching conditions of the respective gas flowrates of SF₆, Cl₂, and O₂ as etching gas of 24 sccm, 12 sccm, and 30sccm, a chamber pressure of 1.3 Pa, an ICP power of 700 W (ICP powerdensity: 1.427 W/cm²), and a bias power of 10 W (bias power density:0.064 W/cm²), and subsequently processing of a second step is performedunder the dry etching conditions of the gas flow rate of Cl₂ as etchinggas of 60 sccm, a chamber pressure of 1.0 Pa, an ICP power of 350 W (ICPpower density: 0.713 W/cm²), and a bias power of 20 W (bias powerdensity: 0.128 W/cm²) (see Tables 2 and 3).

Next, through an ashing process and washing with an organic solvent, theresist pattern 606 b as a mask for dry etching is removed. Thereafter,as a first doping process, an ion doping apparatus is used to implant ann-type impurity including a phosphorus element at a small dosage usingthe first-layer gate electrode 604 b as a mask. Through the first dopingprocess concerned, low concentration impurity regions (n⁻⁻ regions) 607doped with an n-type impurity are formed in portions of thesemiconductor layer 602 corresponding to regions positioned outside thefirst-layer gate electrode 604 b. In this case, the low concentrationimpurity regions (n⁻⁻ regions) 607 are formed by implanting an impuritythrough the gate insulating film 603 b as an upper-layer film using aso-called through-doping method. Note that, the following dopingconditions are conceivable: phosphine (PH₃)/hydrogen (H₂) with phosphine(PH₃) contained at an amount corresponding to a phosphine (PH₃) dilutionratio of 3 to 20% is used as an ion source; an acceleration voltage isset to 30 to 90 kV; and a dosage is set to 6×10¹² to 1.5×10¹⁴ ions/cm².In this embodiment mode, implantation is conducted under the followingdoping conditions: phosphine (PH₃)/hydrogen (H₂) with phosphine (PH₃)contained at an amount corresponding to a phosphine (PH₃) dilution ratioof 5% is used; an acceleration voltage is set to 50 kV; and a dosage isset to 3×10¹³ ions/cm² (see FIG. 8C).

Next, through the general photolithography process, resist patterns 608and 609 as a mask used for doping the impurity are formed. The aboveresist patterns 608 and 609 are formed in regions where a pixel TFT 701of an LDD structure and a p-channel driver circuit 703 of a GOLDstructure are formed, and are not formed in a region where an n-channeldriver circuit 702 of a GOLD structure is formed. In this case, in theregion where the pixel TFT 701 of an LDD structure is formed, the resistpattern 608 is formed such that end portions thereof are positionedinside the semiconductor layer 602 and outside the first-layer gateelectrode 604 b at a predetermined distance therefrom, i.e., such thatthey are positioned outside the end portions of the first-layer gateelectrode 604 b at a distance corresponding to an Loff region (describedin the subsequent steps in detail). Further, in the region where thep-channel driver circuit 703 of a GOLD structure is formed, the resistpattern 609 is formed such that end portions thereof are positionedoutside the semiconductor layer 602, i.e., such that the patterncompletely covers the semiconductor layer 602 (see FIG. 8D).

Subsequently, as a second doping process, the ion doping apparatus isused to implant an n-type impurity including a phosphorus element at alarge dosage. At this time, in the region where the pixel TFT 701 of anLDD structure is formed, through the second doping process concerned,high concentration impurity regions (n⁺ regions) 610 doped with ann-type impurity are formed in portions of the semiconductor layer 602corresponding to regions positioned outside the resist pattern 608. Inthe above semiconductor layer 602, the low concentration impurityregions (n⁻⁻ regions) 607 doped with an n-type impurity have beenformed. However, according to the formation of the high concentrationimpurity regions (n⁺ regions) 610, the above low concentration impurityregions (n⁻⁻ regions) 607 are divided into the high concentrationimpurity regions (n⁺ regions) 610 and low concentration impurity regions(n⁻⁻ regions) 611 formed as a result thereof. The high concentrationimpurity regions (n⁺ regions) 610 thus formed function as a source/drainregion of an LDD structure. The low concentration impurity regions (n⁻⁻regions) 611 function as an electric field relaxation region as the Loffregion (electric field relaxation region overlapped with no gateelectrode) of an LDD structure. On the other hand, in the region wherethe n-channel driver circuit 702 of a GOLD structure is formed, the lowconcentration impurity regions (n⁻⁻ regions) 607 doped with an n-typeimpurity have been formed in portions of the semiconductor layer 602corresponding to regions positioned outside the first-layer gateelectrode 604 b. Further, high concentration impurity regions (n⁺regions) 612 doped with an n-type impurity are formed and at the sametime, low concentration impurity regions (n⁻ regions) 613 doped with ann-type impurity are formed in portions of the semiconductor layer 602corresponding to exposed regions of the first-layer gate electrode 604 bthat protrude from the second-layer gate electrode 605 b. The highconcentration impurity regions (n⁺ regions) 612 thus formed function asa source/drain region of a GOLD structure. The low concentrationimpurity regions (n⁻ regions) 613 function as an electric fieldrelaxation region as an Lov region (electric field relaxation regionoverlapped with the gate electrode) of a GOLD structure. Note that, thefollowing doping conditions are conceivable: phosphine (PH₃)/hydrogen(H₂) with phosphine (PH₃) contained at an amount corresponding to aphosphine (PH₃) dilution ratio of 3 to 20% is used as an ion source; anacceleration voltage is set to 30 to 90 kV; and a dosage is set to6×10¹⁴ to 1.5×10¹⁶ ions/cm². In this embodiment mode, implantation isconducted under the following doping conditions: phosphine(PH₃)/hydrogen (H₂) with phosphine (PH₃) contained at an amountcorresponding to a phosphine (PH₃) dilution ratio of 5% is used; anacceleration voltage is set to 65 kV; and a dosage is set to 3×10¹⁵ions/cm² (see FIG. 8D).

The above high concentration impurity regions (n⁺ regions) 610, 612 andthe low concentration impurity regions (n⁻ regions) 613 are formed byimplanting an impurity through an upper-layer film using a so-calledthrough-doping method. The through-doping method refers to a dopingmethod in which an impurity is implanted into a target substance layerthrough the upper-layer film, with a characteristic in which an impurityconcentration in the target substance layer can be changed depending ona film material and a film thickness of the upper-layer film.Accordingly, in spite of the implantation of the impurity using the samedoping condition, it is possible that the high concentration impurityregions (n⁺ regions) 610, 612 are formed in regions where the gateinsulating film 603 b capable of blocking less ions constitutes anupper-layer film and at the same time, the low concentration impurityregions (n⁻ regions) 613 are formed in regions where a lamination filmconsisting of the first-layer gate electrode (TaN film) 604 b capable ofblocking a large amount of ions and the gate insulating film 603 bconstitutes an upper-layer film. Also, in the lamination film consistingof the first-layer gate electrode (TaN film) 604 b and the gateinsulating film 603 b, which constitutes the upper-layer film of the lowconcentration impurity regions (n⁻ regions) 613, the first-layer gateelectrode (TaN film) 604 b is formed into a tapered shape by taperetching. Thus, the lamination film has a concentration gradient in whichan impurity concentration becomes gradually higher toward the highconcentration impurity regions (n⁺ regions) 612 from the lowconcentration impurity regions (n⁻ regions) 613. Similarly, the gateinsulating film 603 b as an upper-layer film of the high concentrationimpurity regions (n⁺ regions) 612 is also formed into a tapered shape inwhich the film thickness becomes gradually smaller in the regions at thegiven distance from the end portions of the first-layer gate electrode604 b. Thus, the film has the impurity concentration gradient as well(see FIG. 8D).

A detailed description will be further made on generation conditions ofthe above impurity concentration gradient with reference to FIGS. 10Aand 10B. FIG. 10A is a partial enlarged view of the sectional view forshowing a manufacturing step of the n-channel driver circuit 702 of aGOLD structure shown in FIG. 8D. FIG. 10B is a conceptual view showingan impurity concentration distribution in the semiconductor layer. Asapparent from FIG. 10A, the regions corresponding to the exposed regionsof the first-layer gate electrode (TaN film) 604 b which protrude fromthe second-layer gate electrode (W film) 605 b are formed into a taperedshape at a taper angle θ₁ with the film being thinner toward the endportions due to taper etching. For this reason, when the n-type impurityis implanted by the through-doping method, in the low concentrationimpurity regions (n⁻ regions) 613 doped with an n-type impurity whichare located directly below the first-layer gate electrode 604 b, theconcentration gradient is obtained such that the impurity concentrationbecomes gradually higher toward the end portions of the first-layer gateelectrode 604 b as shown in FIG. 10B. In addition, the highconcentration impurity regions (n⁺ regions) 612 doped with an n-typeimpurity and covered only with the gate insulating film 603 b are formedinto a tapered shape at a taper angle θ₂ with the film being graduallythinner in the regions at the given distance from the end portions ofthe first-layer gate electrode 604 b. Thus, the above regions exhibitthe impurity concentration gradient. In this case, it is known that theregions at the given distance from the end portions of the first-layergate electrode 604 b are formed into a tapered shape due to retreatphenomenon of the resist pattern as a mask for dry etching. Note that,the above concentration gradient is highly effective in electric fieldrelaxation in a channel horizontal direction and is extremelyadvantageous in prevention of occurrence of hot carriers as comparedwith the conventional TFT of a GOLD structure having no concentrationgradient.

Next, through an ashing process and washing with an organic solvent, theresist patterns 608 and 609 as masks for the second doping process areremoved. Thereafter, the general photolithography process is performedto form a resist pattern 614 as a mask for doping an impurity. In thiscase, the above resist pattern 614 is formed so as to open on the regionwhere the p-channel driver circuit 703 of a GOLD structure is formed(see FIG. 9A).

Next, as a third doping process, the ion doping apparatus is used toimplant a p-type impurity including a boron element at a large dosage bythe through-doping method. Through the third doping process concerned,in the region where the p-channel driver circuit 703 of a GOLD structureis formed, high concentration impurity regions (p⁺ regions) 615 dopedwith a p-type impurity are formed in portions of the semiconductor layer602 corresponding to regions positioned outside the first-layer gateelectrode 604 b. In addition, in portions of the semiconductor layer 602corresponding to exposed regions of the first-layer gate electrode 604 bwhich protrude from the second-layer gate electrode 605 b, lowconcentration impurity regions (p⁻ regions) 616 doped with a p-typeimpurity are simultaneously formed. The high concentration impurityregions (p⁺ regions) 615 thus formed function as a source/drain regionof a GOLD structure. The low concentration impurity regions (p⁻ regions)616 function as an electric field relaxation region as the Lov region(electric field relaxation region overlapped with the gate electrode) ofa GOLD structure (see FIG. 9A).

Here, in the high concentration impurity regions (p⁺ regions) 615 dopedwith a p-type impurity, the low concentration impurity regions (n⁻⁻regions) 607 doped with an n-type impurity have been formed in advance.However, the p-type impurity is implanted at a concentration equal to orhigher than that of an n-type impurity, so that the high concentrationimpurity regions (p⁺ regions) 615 having a p-type conductivity as awhole are formed. Note that, the high concentration impurity regions (p⁺regions) 615 and the low concentration impurity regions (p⁻ regions) 616which are both doped with a p-type impurity are simultaneously formed bythe through-doping method utilizing the difference in film materials orfilm thicknesses of the upper-layer film in the same manner as in then-type impurity regions. In this case, the following doping conditionsare conceivable: diborane (B₂H₆)/hydrogen (H₂) with diborane (B₂H₆)contained at an amount corresponding to a diborane (B₂H₆) dilution ratioof 3 to 20% is used as an ion source; an acceleration voltage is set to60 to 100 kV; and a dosage is set to 4×10¹⁵ to 1×10¹⁷ ions/cm². In thisembodiment mode, implantation is conducted under the following dopingconditions: diborane (B₂H₆)/hydrogen (H₂) with diborane (B₂H₆) containedat an amount corresponding to a diborane (B₂H6) dilution ratio of 5% isused; an acceleration voltage is set to 80 kV; and a dosage is set to2×10¹⁶ ions/cm² (see FIG. 9A).

Finally, through the ashing process and washing with the organicsolvent, the resist pattern 614 as a mask for the third doping processis removed (see FIG. 9B).

Through the above steps, the semiconductor display device having thepixel TFT 701 of an LDD structure, and the n-channel driver circuit 702and the p-channel driver circuit 703 of a GOLD structure can bemanufactured. In the step of forming the gate electrode in the abovesemiconductor display device, there is adapted a dry etching step ofone-step process or two-step process using an ICP dry etching apparatus.This makes it possible to solve the problems inherent to the prior artin the dry etching step, that is, problems concerning, for example,decrease in throughput in the dry etching step and increase in processcost resulting from consumption amount increase of etching gas, andfurther decrease in yield of a semiconductor device resulting from thecomplicated dry etching step.

EMBODIMENT MODE 2

In this embodiment mode, a description will be given of manufacturingsteps of a semiconductor display device having TFTs of an LDD structureand a GOLD structure, which are different from Embodiment Mode 1 withreference to FIGS. 11A to 12D. Specific circuit configuration in thiscase is similar to that in Embodiment Mode 1. Note that, manufacturingsteps shown in FIGS. 11A and 11B are basically the same as those inEmbodiment Mode 1 (FIGS. 8A and 8B) and thus are shown in a simplemanner.

First, on a glass substrate 801 as a transparent insulating substratewhich is formed in a square shape with a side being 12.5 cm, anisland-like semiconductor layer 802 made of a polycrystalline siliconfilm (crystalline silicon film being substitutable therefor, which isformed utilizing a catalytic element) having a thickness of 50 nm isformed. A gate insulating film 803 a made of a silicon oxide film(silicon oxynitride film being substitutable therefor) having athickness of 100 nm is then deposited so as to cover the abovesemiconductor layer 802. Thereafter, a first-layer gate electrode film804 a made of a TaN film having a thickness of 5 to 50 nm, preferably 20to 40 nm, and a second-layer gate electrode film 805 a made of a W filmhaving a thickness of 200 to 600 nm, preferably 300 to 500 nm, morepreferably 350 to 500 nm are deposited by a sputtering method. In thisembodiment mode, the first-layer gate electrode film 804 a made of a TaNfilm having a thickness of 30 nm and the second-layer gate electrodefilm 805 a made of a W film having a thickness of 370 nm are deposited.The general photolithography process is then performed to form a resistpattern 806 a for forming a gate electrode (see FIG. 11A).

Next, a dry etching process is performed on a metallic laminate filmusing the resist pattern 806 a as a mask through a dry etching step ofone-step process or two-step process, the film including the first-layergate electrode film 804 a and the second-layer gate electrode film 805a. In the dry etching process concerned, since the second-layer gateelectrode 805 b is formed by isotropic etching, the second-layer gateelectrode 805 b is decreased in size in a channel direction as comparedwith the first-layer gate electrode 804 b. Also, portions of thefirst-layer gate electrode 804 b corresponding to exposed regions thatprotrude from the second-layer gate electrode 805 b are formed by taperetching of the dry etching process concerned, and thus are formed into atapered shape while being gradually thinned toward end portions. Also,the gate insulating film 803 b is subjected to etching in regions at agiven distance from the end portions of the first-layer gate electrode804 b due to film reduction in dry etching and is formed into a taperedshape. As the distance from the first-layer gate electrode 804 bincreases, the film becomes thinner and further, a residual filmthickness is maintained as a given thickness outside the above regionsat the given distance. Note that, it is assumed that the regions at thegiven distance therefrom are formed into a tapered shape due to retreatphenomenon of the resist pattern (the resist pattern 806 a retreatingtoward the resist pattern 806 b) in dry etching (see FIG. 11B).

Here, for the above dry etching step, a dry etching method utilizinghigh density plasma which can independently control plasma density and abias voltage applied to a subject substrate is suitable. Our companyemploys an ICP dry etching apparatus. Specific conditions of dry etchingin the ICP dry etching apparatus concerned are as follows. That is,although differing between the dry etching step of one-step process andthat of two-step process, the conditions employ dry etching conditionsshown in Table 2 in the case of one-step process and employ those shownin Table 3 in the case of two-step process. In other words, in the caseof dry etching step of one-step process, processing is performed underthe etching conditions of the respective gas flow rates of SF₆, Cl₂, andO₂ as etching gas of 24 sccm, 12 sccm, and 24 sccm (corresponding to theoxygen addition amount of 40%), a chamber pressure of 1.3 Pa, an ICPpower of 700 W (ICP power density: 1.427 W/cm²), and a bias power of 10W (bias power density: 0.064 W/cm²). On the other hand, in the case ofdry etching step of two-step process, processing of a first step isperformed under the dry etching conditions of the respective gas flowrates of SF₆, Cl₂, and O₂ as etching gas of 24 sccm, 12 sccm, and 30sccm, a chamber pressure of 1.3 Pa, an ICP power of 700 W (ICP powerdensity: 1.427 W/cm²), and a bias power of 10 W (bias power density:0.064 W/cm²), and subsequently processing of a second step is performedunder the dry etching conditions of the gas flow rate of Cl₂ as etchinggas of 60 sccm, a chamber pressure of 1.0 Pa, an ICP power of 350 W (ICPpower density: 0.713 W/cm²), and a bias power of 20 W (bias powerdensity: 0.128 W/cm²) (see Tables 2 and 3).

Next, as a first doping process, an ion doping apparatus is used toimplant an n-type impurity including a phosphorus element at a largedosage. Through the first doping process concerned, high concentrationimpurity regions (n⁺ regions) 807 doped with an n-type impurity areformed by the through-doping method in portions of the semiconductorlayer 802 corresponding to regions positioned outside the resist pattern806 b, i.e., outside the first-layer gate electrode 804 b. In this case,the following doping conditions are conceivable: phosphine(PH₃)/hydrogen (H₂) with phosphine (PH₃) contained at an amountcorresponding to a phosphine (PH₃) dilution ratio of 3 to 20% is used asan ion source; an acceleration voltage is set to 60 to 100 kV; and adosage is set to 2×10¹⁴ to 5×10 ¹⁵ ions/cm². In this embodiment mode,implantation is conducted under the following doping conditions:phosphine (PH₃)/hydrogen (H₂) with phosphine (PH₃) contained at anamount corresponding to a phosphine (PH₃) dilution ratio of 5% is used;an acceleration voltage is set to 80 kV; and a dosage is set to 1×10¹⁵ions/cm² (see FIG. 11C).

Next, through an ashing process and washing with an organic solvent, theresist pattern 806 b as a mask for the dry etching process and the firstdoping process is removed. Thereafter, as a second doping process, theion doping apparatus is used to implant an n-type impurity including aphosphorus element at a small dosage using the second-layer gateelectrode 805 b as a mask. Through the second doping process concerned,low concentration impurity regions (n⁻ regions) 809 doped with an n-typeimpurity are formed by the through-doping method in portions of thesemiconductor layer 802 corresponding to exposed regions of thefirst-layer gate electrode 804 b which protrude from the second-layergate electrode 805 b. Also, in portions of the semiconductor layer 802corresponding to regions positioned outside the first-layer gateelectrode 804 b, the high concentration impurity regions (n⁺ regions)807 doped with an n-type impurity have been formed. However, since ann-type impurity is implanted into the above regions at a small dosage,high concentration impurity regions (n⁺ regions) 808 are formed with aconcentration of the n-type impurity further increased. Note that, thefollowing doping conditions are conceivable: phosphine (PH₃)/hydrogen(H₂) with phosphine (PH₃) contained at an amount corresponding to aphosphine (PH₃) dilution ratio of 3 to 20% is used as an ion source; anacceleration voltage is set to 60 to 100 kV; and a dosage is set to3×10¹³ to 7.5×10¹⁴ ions/cm². In this embodiment mode, implantation isconducted under the following doping conditions: phosphine(PH₃)/hydrogen (H₂) with phosphine (PH₃) contained at an amountcorresponding to a phosphine (PH₃) dilution ratio of 5% is used; anacceleration voltage is set to 90 kV; and a dosage is set to 1.5×10¹⁴ions/cm² (see FIG. 11D).

Through the steps up to this step, in a region where an n-channel drivercircuit 902 of a GOLD structure is manufactured, there is completed theformation of the high concentration impurity regions (n⁺ regions) 808doped with an n-type impurity which function as a source/drain regionand the low concentration impurity regions (n⁻ regions) 809 doped withan n-type impurity which function as an electric field relaxation regionas an Lov region (electric field relaxation region overlapped with thegate electrode).

Next, the general photolithography process is performed to form a resistpattern 810 serving as a mask for a dry etching process. In this case,the above resist pattern 810 is formed so as to open on a region where apixel TFT 901 of an LDD structure is formed. Subsequently, in the aboveopening, the second-layer gate electrode 805 b made of a W film is usedas a mask to remove the first-layer gate electrode 804 b made of a TaNfilm by the dry etching process. The ICP dry etching apparatus isadapted for the above dry etching process so that there are employed dryetching conditions under which the film reduction of the W film issuppressed. As specific conditions of dry etching, the same conditionsas those in the second step among the dry etching conditions shown inTable 3 can be employed for processing. That is, the dry etching processis conducted for a predetermined period of time under the dry etchingconditions of the gas flow rate of Cl₂ as etching gas of 60 sccm, achamber pressure of 1.0 Pa, an ICP power of 350 W (ICP power density:0.713 W/cm²), and a bias power of 20 W (bias power density: 0.128 W/cm²)(see FIG. 12A and Table 3).

Through the steps up to this step, in a region where the pixel TFT 901of an LDD structure is formed, there is completed the formation of thehigh concentration impurity regions (n⁺ regions) 808 doped with ann-type impurity which function as a source/drain region and the lowconcentration impurity regions (n⁻ regions) 809 doped with an n-typeimpurity which function as an electric field relaxation region as anLoff region (electric field relaxation region overlapped with no gateelectrode).

Next, through the ashing process and washing with an organic solvent,the resist pattern 810 used as the mask for the dry etching process isremoved. Thereafter, a generally used RIE system dry etching apparatusis used to perform a dry etching process for a predetermined period oftime, so that the entire exposed regions of the gate insulating film 803b made of a silicon oxide film are etched back (thinned throughetching). Through the above etch-back process, in the region where thepixel TFT 901 of an LDD structure is formed, the gate insulating film isetched back into a shape of a gate insulating film 812, and in theregion where the n-channel driver circuit 902 of a GOLD structure isformed or in a region where a p-channel driver circuit 903 of a GOLDstructure is formed, the gate insulating film is etched back into ashape of a gate insulating film 813. Note that, the above etch-backprocess is performed in order to increase implantation efficiency inimplanting a boron element at a large dosage in the subsequent steps fordoping process of a p-type impurity. Specific conditions of dry etchingare as follows: a gas flow rate of CHF₃ as etching gas is 35 sccm; achamber pressure is 7.3 Pa; and an RF power is 800 W (RF power density:1.28 W/cm²). Under these conditions, the dry etching process isperformed for a predetermined period of time. In addition, the aboveetch-back process is conducted according to not an end point detectionmethod but a time-based etching method, so that it is required tomonitor an etching rate under control. Note that, as for the dry etchingapparatus used for the above etch-back process, a batch process for foursubject substrates (square substrates with a side being 12.5 cm) isemployed, so that the RF power density is calculated through division ofthe RF power (80 W) by a total area of the four subject substrates(4×12.5×12.5 cm²) (see FIG. 12B).

Next, the general photolithography process is performed to form a resistpattern 814 serving as a mask for doping an impurity. In this case, theabove resist pattern 814 is formed so as to open on the region where thep-channel driver circuit 903 of a GOLD structure is formed. Thereafter,as a third doping process, the ion doping apparatus is used to implant ap-type impurity including a boron element by the through-doping method.In the above third doping process, the doping process is performed intwo stages. In this case, a doping process at a low acceleration and alarge dosage and a doping process at a high acceleration and a smalldosage are performed. The doping process is performed in two stagesbecause the preceding etch-back process of the gate insulating film 803b makes larger a difference in an ion blocking ability of theupper-layer film between the region where the high concentrationimpurity region is formed and the region where the low concentrationimpurity region is formed, which makes it difficult to simultaneouslyform the high concentration impurity region (p⁺ region) and the lowconcentration impurity region (p⁻ region) at one doping process. Throughsuch a doping process at a low acceleration and a large dosage, in aregion where the p-channel driver circuit 903 is formed, highconcentration impurity regions (p⁺ regions) 815 are formed in portionsof the semiconductor layer 802 corresponding to regions positionedoutside the first-layer gate electrode 804 b. Also, through the dopingprocess at a high acceleration and a small dosage, low concentrationimpurity regions (p⁻ regions) 816 doped with a p-type impurity areformed in portions of the semiconductor layer 802 corresponding toexposed regions of the first-layer gate electrode 804 b which protrudefrom the second-layer gate electrode 805 b. Note that, the above highconcentration impurity regions (p⁺ regions) 815 are formed so as tofunction as a source/drain region of a GOLD structure. The above lowconcentration impurity regions (p⁻ regions) 816 are formed so as tofunction as an electric field relaxation region as the Lov region(electric field relaxation region overlapped with the gate electrode) ofa GOLD structure (see FIG. 12C).

Here, in the high concentration impurity regions (p⁺ regions) 815 andthe low concentration impurity regions (p⁻ regions) 816 which are bothdoped with a p-type impurity, the high concentration impurity regions(n⁺ regions) 808 and the low concentration impurity regions (n⁻ regions)809 which are both doped with an n-type impurity are respectivelyformed. However, the p-type impurity is implanted into the respectiveimpurity regions at an impurity concentration twice or more the n-typeimpurity concentration, so that the high concentration impurity regions(p⁺ regions) 815 and the low concentration impurity regions (p⁻ regions)816 are formed having a p-type conductivity as a whole. Note that, asthe doping conditions at a low acceleration and a large dosage, thefollowing are conceivable: diborane (B₂H6)/hydrogen (H₂) with diborane(B₂H₆) contained at an amount corresponding to a diborane (B₂H₆)dilution ratio of 3 to 20% is used as an ion source; an accelerationvoltage is set to 20 to 50 kV; and a dosage is set to 4×10¹⁴ to 1×10¹⁶ions/cm². In this embodiment mode, implantation is conducted under thefollowing doping conditions: diborane (B₂H₆)/hydrogen (H₂) with diborane(B₂H₆) contained at an amount corresponding to a diborane (B₂H₆)dilution ratio of 5% is used; an acceleration voltage is set to 30 kV;and a dosage is set to 2×10¹⁵ ions/cm². Also, as the doping conditionsat a high acceleration and a small dosage, the following are conceivablewithout changing the ion source: an acceleration voltage is set to 60 to100 kV; and a dosage is set to 1.8×10¹⁴ to 4.5×10¹⁵ ions/cm^(2.) In thisembodiment mode, implantation is conducted under the following dopingconditions: diborane (B₂H₆)/hydrogen (H₂) with diborane (B₂H₆) containedat an amount corresponding to a diborane (B₂H₆) dilution ratio of 5% isused; an acceleration voltage is set to 80 kV; and a dosage is set to9×10¹⁴ ions/cm² (see FIG. 12C).

Finally, through the ashing process and washing with the organicsolvent, the resist pattern 814 as a mask for the third doping processis removed (see FIG. 12D).

Through the above steps, the semiconductor display device having thepixel TFT 901 of an LDD structure, and the n-channel driver circuit 902and the p-channel driver circuit 903 of a GOLD structure can bemanufactured. In the step of forming the gate electrode in the abovesemiconductor display device, there is adapted a dry etching step ofone-step process or two-step process using an ICP dry etching apparatus.This makes it possible to solve the problems inherent to the prior artin the dry etching step, that is, problems concerning, for example,decrease in throughput in the dry etching step and increase in processcost resulting from consumption amount increase of etching gas, andfurther decrease in yield of a semiconductor device resulting from thecomplicated dry etching step.

EMBODIMENT 1

In this embodiment, a specific description will be given of amanufacturing method for an active matrix liquid crystal display deviceusing the present invention with reference to FIGS. 13A to 18B. Notethat this embodiment basically employs the same manufacturing method asin Embodiment Mode 1 except that a crystalline silicon film crystallizedusing a catalytic element is adapted for the semiconductor layer as anactive layer of the TFT instead of using the general polycrystallinesilicon film.

First, on a glass substrate 1001 are deposited by a plasma CVD methodsilicon oxynitride films 1002 a and 1002 b as a first layer with athickness of 50 nm and a second layer with a thickness of 100 nm,respectively, with different composition ratios, so as to constitute abase film 1002. Note that, the glass substrate 1001 used in this casemay be made of quartz glass, barium borosilicate glass,aluminoborosilicate glass, etc. Next, on the base film 1002 (1002 a and1002 b), an amorphous silicon film 1003 a having a thickness of 20 to200 nm, preferably 30 to 70 nm, is deposited by a plasma CVD method or areduced pressure CVD method. In this embodiment, the amorphous siliconfilm 1003 a having a thickness of 53 nm is deposited by the plasma CVDmethod. In this case, on a surface of the amorphous silicon film 1003 a,an extremely thin natural oxide film (not shown) is formed due to oxygenin the air mixed into a process atmosphere. Note that, in thisembodiment, the amorphous silicon film 1003 a is deposited by the plasmaCVD method, but it may be deposited by the reduced pressure CVD method(see FIG. 13A).

Here, upon the deposition of the amorphous silicon film 1003 a, there isa possibility that carbon, oxygen, and nitrogen in the air are mixedtherein. It is experientially known that these impurity gases mixedtherein cause characteristic deterioration of TFTs finally obtained andthey supposedly act as a factor for inhibiting crystallization.Accordingly, it is required to completely prevent the impurity gas frommixing therein. Specifically, in the case of the carbon and thenitrogen, both are preferably controlled to 5×10¹⁷ atoms/cm³ or less andin the case of oxygen, it is preferably controlled to 1×10¹⁸ atoms/cm³or less (see FIG. 13A).

Next, the above substrate is washed with a diluted hydrofluoric acid fora predetermined period of time to remove the natural oxide film (notshown) formed on the surface of the amorphous silicon film 1003 a.Following this, treatment with ozone water is performed for apredetermined period of time to lightly oxidize the surface of theamorphous silicon film 1003 a. A clean and extremely thin silicon oxidefilm (not shown) is formed on the surface of the amorphous silicon film1003 a by the above light oxidization process. Also, the extremely thinsilicon oxide film (not shown) may be formed by treatment with ahydrogen peroxide solution. Note that, the extremely thin silicon oxidefilm (not shown) is formed for the purpose of improving a wettabilitywith respect to the amorphous silicon film 1003 a such that, when anitrogen element solution as a solution containing a catalytic element(hereinafter, abbreviated to catalytic element solution) is appliedthereto by a spin-coating method later, the nitrogen element isuniformly attached thereto (see FIG. 13A).

Next, onto the entire surface of the amorphous silicon film 1003 a (moreprecisely, the extremely thin silicon oxide film), the catalytic elementsolution including a nitrogen element solution having an action ofpromoting crystallization is applied by a spin-coating method. In thisembodiment, a nickel acetate salt as a nickel compound is dissolved intopure water to be adjusted into a concentration of 10 ppm in terms ofweight, and the resultant is used as a nickel element solution. Thenickel containing layer (not shown) is uniformly attached onto theentire surface of the amorphous silicon film 1003 a (more precisely, theextremely thin silicon oxide film) (see FIG. 13A).

Next, in order to control the hydrogen content in the amorphous siliconfilm 1003 a to 5 atoms % or less, a dehydrogenation process is performedon hydrogen contained in the amorphous silicon film 1003 a. The abovedehydrogenation process is achieved by heat treatment using an annealingfurnace in a nitrogen atmosphere at 450° C. for 1 hour. Thereafter, heattreatment in the annealing furnace at 550° C. for 4 hours is performedto promote crystallization of the amorphous silicon film 1003 a to forma crystalline silicon film 1003 b having a thickness of 50 nm.Subsequently, in order to further improve the crystallinity of theobtained crystalline silicon film 1003 b, a KrF excimer laser of pulseoscillation (wavelength: 248 nm) is irradiated to crystallize the film.Note that, in this specification, in order to distinguish apolycrystalline silicon film crystallized using a nickel element as acatalytic element from the general polycrystalline silicon film, thefilm is called the crystalline silicon film. Here, the reason foremploying the term crystalline instead of the term polycrystalline isthat, in the film of the present invention, since crystal grains areoriented substantially in the same direction with high field effectmobility as characteristics thereof as compared with the generalpolycrystalline silicon film, the film is distinguished from the generalpolycrystalline silicon film (see FIG. 13A).

Next, washing prior to channel doping is performed by washing with adiluted hydrofluoric acid and ozone water for a predetermined period oftime to form an extremely thin silicon oxide film (not shown) on thesurface of the crystalline silicon film 1003 b. The above extremely thinsilicon oxide film (not shown) is formed for the purpose of preventingthe crystalline silicon film 1003 b from being etched due to hydrogenions (generated from a mixed gas of diborane (B₂H₆) and hydrogen as anion source) in the channel doping process. In order to control thethreshold voltage of the n-channel and p-channel TFTs, the channeldoping process as a first doping process is then conducted using an iondoping apparatus. The channel doping process is performed by implantinga p-type impurity (specifically, boron element) into the entiresubstrate surface at a small dosage. In this case, the following dopingconditions are conceivable: diborane (B₂H₆)/hydrogen (H₂) with diborane(B₂H₆) contained at an amount corresponding to a diborane (B₂H₆)dilution ratio of 0.01 to 1% is used as an ion source; an accelerationvoltage is set to 5 to 30 kV; and a dosage is set to 8×10¹³ to 2×10¹⁵ions/cm². In this embodiment, in order to set a boron concentration inthe crystalline silicon film 1003 b to about 1×10¹⁷ atoms/cm³,implantation of the boron element is conducted under the followingdoping conditions: diborane (B₂H₆)/hydrogen (H₂) with diborane (B₂H₆)contained at an amount corresponding to a diborane (B₂H₆) dilution ratioof 0.1% is used; an acceleration voltage is set to 15 kV; and a dosageis set to 4×10¹⁴ ions/cm² (see FIG. 13B).

Next, generally used photolithography and dry etching processes arepreformed to conduct the pattern formation on the crystalline siliconfilm 1003 b to thereby form island-like semiconductor layers 1004 to1008 with a predetermined pattern shape and a predetermined size. Notethat, the above semiconductor layers 1004 to 1008 are used to form asource/drain region and a channel region of the TFT in the subsequentsteps (see FIG. 13B).

Next, a silicon oxide film or a silicon oxynitride film is deposited asa gate insulating film 1009 with a thickness of 30 to 200 nm, preferably80 to 130 nm by a plasma CVD method or a reduced pressure CVD method soas to cover the semiconductor layers 1004 to 1008. In this embodiment,the gate insulating film 1009 made of a silicon oxide film having athickness of 100 nm is deposited by a plasma CVD method. Note that, itis known that the gate insulating film 1009 is required to have athickness of 80 nm or more to avoid a stress applied from a gateelectrode (gate electrode made of lamination of a W film and a TaN film)located in an upper layer. Thus, it is determined while taking intoaccount this point (see FIG. 14A).

Next, in order to deposit a metallic laminate film for a gate electrode,a first-layer gate electrode film 1010 and a second-layer gate electrodefilm 1011 are continuously deposited by a sputtering method. Thefirst-layer gate electrode film 1010 can be made of a TaN film with athickness of 5 to 50 nm, preferably 20 to 40 nm. In this embodiment, theTaN film having a thickness of 30 nm is deposited. The second-layer gateelectrode film 1011 can be made of a W film with a thickness of 200 to600 nm, preferably 300 to 500 nm, more preferably 350 to 500 nm. In thisembodiment, the W film having a thickness of 370 nm is deposited. Notethat, the thickness of the TaN film is determined while considering bothof controllability of a residual film thickness in a taper-shaped regionupon dry etching and implantation characteristics upon implantation ofan impurity element through the TaN film by a through-doping method.Further, it is known that the W film is required to have a thickness of340 nm or more in order to prevent channeling phenomenon from occurringin the W film upon the implantation of the impurity element. Thus, it isdetermined while taking into account this point (see FIG. 14A).

Next, the general photolithography process is conducted to form resistpatterns 1012 a to 1017 a having a predetermined size on the metalliclaminate film. Note that, the resist patterns 1012 a to 1017 a are usedfor forming a gate electrode, an electrode for a storage capacitor, asource wiring, and the like (see FIG. 14B).

The dry etching process is performed on the metallic laminate filmconsisting of the first-layer gate electrode film 1010 made of a TaNfilm with a thickness of 30 nm and the second-layer gate electrode film1011 made of a W film with a thickness of 370 nm using the resistpatterns 1012 a to 1017 a as masks. At this time, a dry etching step ofone-step process or two-step process is adapted to the above dry etchingprocess. Gate electrodes consisting of first-layer gate electrodes 1012d to 1015 d and second-layer gate electrodes 1012 c to 1015 c with apredetermined size are formed. At the same time, there are formed astorage capacitor electrode with a predetermined size consisting of afirst-layer storage capacitor electrode 1016 d and a second-layerstorage capacitor electrode 1016 c, and a source wiring electrode with apredetermined size consisting of a first-layer source wiring electrode1017 d and a second-layer source wiring electrode 1017 c. In the dryetching process concerned, since second-layer electrodes 1012 c to 1017c (generic term for the electrodes consisting of the second-layer gateelectrodes 1012 c to 1015 c, the second-layer storage capacitorelectrode 1016 c, and the second-layer source wiring electrode 1017 c)are formed by isotropic etching, so that the second-layer electrodes1012 c to 1017 c are decreased in size in a channel direction comparedwith first-layer electrodes 1012 d to 1017 d (generic term for theelectrodes consisting of the first-layer gate electrodes 1012 d to 1015d, the first-layer storage capacitor electrode 1016 d, and thefirst-layer source wiring electrode 1017 d). Also, portions of thefirst-layer electrodes 1012 d to 1017 d corresponding to exposed regionsthat protrude from the second-layer electrodes 1012 c to 1017 c areformed by taper etching of the dry etching process concerned, and thusare formed into a tapered shape while being gradually thinned toward theend portions. Also, the gate insulating film 1018 is subjected toetching in regions at a given distance from the end portions of thefirst-layer electrodes 1012 d to 1017 d due to film reduction in dryetching and is formed into a tapered shape. As the distance from thefirst-layer electrodes 1012 d to 1017 d increases, the film becomesthinner and further, a residual film thickness is maintained as a giventhickness outside the above regions at the given distance. In addition,after development, the resist patterns 1012 a to 1017 a are changed intoresist patterns 1012 b to 1017 b in shape due to film reduction in dryetching (see FIG. 15A).

Here, for the above dry etching step, a dry etching method utilizinghigh density plasma which can independently control plasma density and abias voltage applied to a subject substrate is suitable. Our companyemploys an ICP dry etching apparatus. Specific conditions of dry etchingin the ICP dry etching apparatus concerned are as follows. That is,although differing between the dry etching step of one-step process andthat of two-step process, the conditions employ dry etching conditionsshown in Table 2 in the case of one-step process and employ those shownin Table 3 in the case of two-step process. In other words, in the caseof dry etching step of one-step process, processing is performed underthe etching conditions of the respective gas flow rates of SF₆, Cl₂, andO₂ as etching gas of 24 sccm, 12 sccm, and 24 sccm (corresponding to theoxygen addition amount of 40%), a chamber pressure of 1.3 Pa, an ICPpower of 700 W (ICP power density: 1.427 W/cm²), and a bias power of 10W (bias power density: 0.064 W/cm²). On the other hand, in the case ofdry etching step of two-step process, processing of a first step isperformed under the dry etching conditions of the respective gas flowrates of SF₆, Cl₂, and O₂ as etching gas of 24 sccm, 12 sccm, and 30sccm, a chamber pressure of 1.3 Pa, an ICP power of 700 W (ICP powerdensity: 1.427 W/cm²), and a bias power of 10 W (bias power density:0.064 W/cm²), and subsequently processing of a second step is performedunder the dry etching conditions of the gas flow rate of Cl₂ as etchinggas of 60 sccm, a chamber pressure of 1.0 Pa, an ICP power of 350 W (ICPpower density: 0.713 W/cm²), and a bias power of 20 W (bias powerdensity: 0.128 W/cm²) (see Tables 2 and 3).

Next, through an ashing process and washing with an organic solvent, theresist patterns 1012 b to 1017 b as a mask for dry etching are removed.Thereafter, as a second doping process, an ion doping apparatus is usedto implant an n-type impurity including a phosphorus element at a smalldosage using the first-layer electrodes 1012 d to 1016 d as a mask.Through the second doping process concerned, low concentration impurityregions (n⁻⁻ regions) 1019 to 1023 doped with an n-type impurity areformed in portions of the semiconductor layers 1004 to 1008corresponding to regions positioned outside the first-layer electrodes1012 d to 1016 d. In this case, the low concentration impurity regions(n⁻⁻ regions) 1019 to 1023 are formed by implanting an impurity throughthe gate insulating film 1018 as an upper-layer film using a so-calledthrough-doping method. Note that, the following doping conditions areconceivable: phosphine (PH₃)/hydrogen (H₂) with phosphine (PH₃)contained at an amount corresponding to a phosphine (PH₃) dilution ratioof 3 to 20% is used as an ion source; an acceleration voltage is set to30 to 90 kV; and a dosage is set to 6×10¹² to 1.5×10¹⁴ ions/cm². In thisembodiment, implantation is conducted under the following dopingconditions: phosphine (PH₃)/hydrogen (H₂) with phosphine (PH₃) containedat an amount corresponding to a phosphine (PH₃) dilution ratio of 5% isused; an acceleration voltage is set to 50 kV; and a dosage is set to3×10¹³ ions/cm² (see FIG. 15B).

Next, through the general photolithography process, resist patterns 1024and 1025 as a mask used for doping the impurity are formed. The aboveresist patterns 1024 and 1025 are formed in regions where a p-channelTFT 1102 constituting a driver circuit 1106 of a GOLD structure and apixel TFT 1104 of an LDD structure are formed, and are not formed inregions where n-channel TFTs 1101 and 1103 constituting the drivercircuit 1106 of a GOLD structure and a storage capacitor 1105 areformed. In this case, in the region where the p-channel TFT 1102 of aGOLD structure is formed, the resist pattern 1024 is formed such thatend portions thereof are positioned outside the semiconductor layer1005, i.e., such that the pattern completely covers the semiconductorlayer 1005. In addition, in the region where the pixel TFT 1104 of anLDD structure is formed, the resist pattern 1025 is formed such that endportions thereof are positioned inside the semiconductor layer 1007 andoutside the first-layer gate electrode 1015 d at a given distancetherefrom, i.e. such that they are positioned outside end portions ofthe first-layer gate electrode 1015 d at a distance corresponding to anLoff region (described in the subsequent steps in detail) (see FIG.16A).

Subsequently, as a third doping process, the ion doping apparatus isused to implant an n-type impurity including a phosphorus element at alarge dosage. At this time, in the regions where the n-channel TFTs 1101and 1103 constituting the driver circuit 1106 of a GOLD structure areformed, in portions of the semiconductor layers 1004 and 1006corresponding to regions positioned outside the first-layer gateelectrodes 1012 d and 1014 d, the low concentration impurity regions(n⁻⁻ regions) 1019 and 1021 doped with an n-type impurity have beenformed. Further, high concentration impurity regions (n⁺ regions) 1026and 1028 doped with an n-type impurity are formed and at the same time,low concentration impurity regions (n⁻ regions) 1027 and 1029 doped withan n-type impurity are formed in portions of the semiconductor layers1004 and 1006 corresponding to exposed regions of the first-layer gateelectrodes 1012 d and 1014 d that protrude from the second-layer gateelectrodes 1012 c and 1014 c. The high concentration impurity regions(n⁺ regions) 1026 and 1028 thus formed function as a source/drain regionof a GOLD structure. The low concentration impurity regions (n⁻ regions)1027 and 1029 function as an electric field relaxation region as an Lovregion (electric field relaxation region overlapped with the gateelectrode) of a GOLD structure. Also in the region where the storagecapacitor 1105 is formed, high concentration impurity regions (n⁺regions) 1032 and low concentration impurity regions (n⁻ regions) 1033which are both doped with an n-type impurity are similarly formed. Thethus formed high concentration impurity regions (n⁺ regions) 1032 andlow concentration impurity regions (n⁻ regions) 1033 which are bothdoped with an n-type impurity function as one electrode for forming acapacitor because the above regions are regions where the storagecapacitor 1105 is formed instead of the TFT (see FIG. 16A).

On the other hand, in the region where the pixel TFT 1104 of an LDDstructure is formed, through the above third doping process, highconcentration impurity regions (n⁺ regions) 1030 doped with an n-typeimpurity are formed in portions of the semiconductor layer 1007corresponding to regions positioned outside the resist pattern 1025. Inthe above semiconductor layer 1007, the low concentration impurityregions (n⁻⁻ regions) 1022 doped with an n-type impurity have beenformed. However, according to the formation of the high concentrationimpurity regions (n⁺ regions) 1030, the above low concentration impurityregions (n⁻⁻ regions) 1022 are divided into the high concentrationimpurity regions (n⁺ regions) 1030 and low concentration impurityregions (n⁻⁻ regions) 1031 formed as a result thereof. The highconcentration impurity regions (n⁺ regions) 1030 thus formed function asa source/drain region of an LDD structure. The low concentrationimpurity regions (n⁻⁻ regions) 1031 function as an electric fieldrelaxation region as the Loff region (electric field relaxation regionoverlapped with no gate electrode) of an LDD structure. Note that, thefollowing doping conditions are conceivable: phosphine (PH₃)/hydrogen(H₂) with phosphine (PH₃) contained at an amount corresponding to aphosphine (PH₃) dilution ratio of 3 to 20% is used as an ion source; anacceleration voltage is set to 30 to 90 kV; and a dosage is set to6×10¹⁴ to 1.5×10¹⁶ ions/cm². In this embodiment, implantation isconducted under the following doping conditions: phosphine(PH₃)/hydrogen (H₂) with phosphine (PH₃) contained at an amountcorresponding to a phosphine (PH₃) dilution ratio of 5% is used; anacceleration voltage is set to 65 kV; and a dosage is set to 3×10¹⁵ions/cm² (see FIG. 16A).

The above high concentration impurity regions (n⁺ regions) 1026, 1028,1030, and 1032 and low concentration impurity regions (n⁻ regions) 1027,1029, and 1033 are formed by implanting an impurity through anupper-layer film using a so-called through-doping method. Thethrough-doping method refers to a doping method in which an impurity isimplanted into a target substance layer through the upper-layer film,with a characteristic in which an impurity concentration in the targetsubstance layer can be changed depending on a material and a thicknessof the upper-layer film. Accordingly, in spite of the implantation ofthe impurity using the same doping conditions, it is possible that thehigh concentration impurity regions (n⁺ regions) 1026, 1028, 1030, and1032 are formed in regions where the gate insulating film 1018 capableof blocking less ions constitutes an upper-layer film and at the sametime, the low concentration impurity regions (n⁻ regions) 1027, 1029,and 1033 are formed in regions where a lamination film consisting of thefirst-layer electrodes (TaN films) 1012 d, 1014 d, and 1016 d capable ofblocking a large amount of ions and the gate insulating film 1018constitutes an upper-layer film. Also, in the lamination film consistingof the first-layer electrodes (TaN films) 1012 d, 1014 d, and 1016 d andthe gate insulating film 1018, which constitutes the upper-layer film ofthe low concentration impurity regions (n⁻ regions) 1027, 1029, and1033, the first-layer electrodes (TaN films) 1012 d, 1014 d, and 1016 dare formed into a tapered shape by taper etching. Thus, the laminationfilm has a concentration gradient in which an impurity concentrationbecomes gradually higher toward the high concentration impurity regions(n⁺ regions) 1026, 1028, and 1032 from the low concentration impurityregions (n⁻ regions) 1027, 1029, and 1033. Similarly, the gateinsulating film 1018 as an upper-layer film of the high concentrationimpurity regions (n⁺ regions) 1026, 1028, and 1032 is also formed into atapered shape in which the film thickness becomes gradually smaller inthe regions at the given distance from the end portions of thefirst-layer electrodes 1012 d, 1014 d, and 1016 d. Thus, the film hasthe impurity concentration gradient as well (see FIG. 16A).

Note that, in the regions where the n-channel TFTs 1101 and 1103constituting the driver circuit 1106 of a GOLD structure are formed, inassociation with the formation of the above high concentration impurityregions (n⁺ regions) 1026, 1028 and the low concentration impurityregions (n⁻ regions) 1027, 1029, regions of the semiconductor layers1004 and 1006 overlapped with the second-layer gate electrodes 1012 cand 1014 c are defined as channel regions of the TFTs. Also, in theregion where the pixel TFT 1104 of an LDD structure is formed, a regionof the semiconductor layer 1007 overlapped with the first-layer gateelectrode 1015 d is defined as a channel region of the TFT in the samemanner.

Next, through an ashing process and washing with an organic solvent, theresist patterns 1024 and 1025 as masks for the third doping process areremoved. Thereafter, the general photolithography process is performedto form resist patterns 1034 to 1036 as a mask for doping an impurity.In this case, the above resist patterns 1034 to 1036 are formed so as toopen on the regions where the p-channel TFT 1102 constituting the drivercircuit 1106 of a GOLD structure and the storage capacitor 1105 areformed (see FIG. 16B).

Next, as a fourth doping process, the ion doping apparatus is used toimplant a p-type impurity including a boron element at a large dosage bythe through-doping method. Through the fourth doping process concerned,in the region where the p-channel TFT 1102 constituting the drivercircuit 1106 of a GOLD structure is formed, high concentration impurityregions (p⁺ regions) 1037 doped with a p-type impurity are formed inportions of the semiconductor layer 1005 corresponding to regionspositioned outside the first-layer gate electrode 1013 d. In addition,in portions of the semiconductor layer 1005 corresponding to exposedregions of the first-layer gate electrode 1013 d which protrude from thesecond-layer gate electrode 1013 c, low concentration impurity regions(p⁻ regions) 1038 doped with a p-type impurity are simultaneouslyformed. The high concentration impurity regions (p⁺ regions) 1037 thusformed function as a source/drain region of a GOLD structure. The lowconcentration impurity regions (p⁻ regions) 1038 function as an electricfield relaxation region as the Lov region (electric field relaxationregion overlapped with the gate electrode) of a GOLD structure. On theother hand, also in the region where the storage capacitor 1105 isformed, high concentration impurity regions (p⁺ regions) 1039 and lowconcentration impurity regions (p⁻ regions) 1040 are formed, whichfunction as one electrode for forming a capacitor in the same manner(see FIG. 16B).

Here, in the high concentration impurity regions (p⁺ regions) 1037 dopedwith a p-type impurity in the region where the p-channel TFT 1102 isformed, the low concentration impurity regions (n⁻⁻ regions) 1020 dopedwith an n-type impurity have been formed. However, the p-type impurityis implanted at a concentration equal to or higher than that of ann-type impurity, so that the high concentration impurity regions (p⁺regions) 1037 having a p-type conductivity as a whole are formed. Also,the high concentration impurity regions (n⁺ regions) 1032 and the lowconcentration impurity regions (n⁻ regions) 1033 which are both dopedwith a n-type impurity have been formed also in the region where thestorage capacitor 1105 is formed. However, the p-type impurity isimplanted at a concentration equal to or higher than that of an n-typeimpurity, so that the high concentration impurity regions (p⁺ regions)1039 and the low concentration impurity regions (p⁻ regions) 1040 havinga p-type conductivity as a whole are formed. Note that, the highconcentration impurity regions (p⁺ regions) 1037, 1039 and the lowconcentration impurity regions (p⁻ regions) 1038, 1040 which are bothdoped with a p-type impurity are simultaneously formed by thethrough-doping method utilizing the difference in film material or filmthickness of the upper-layer film in the same manner as in the n-typeimpurity regions. In this case, the following doping conditions areconceivable: diborane (B₂H₆)/hydrogen (H₂) with diborane (B₂H₆)contained at an amount corresponding to a diborane (B₂H₆) dilution ratioof 3 to 20% is used as an ion source; an acceleration voltage is set to60 to 100 kV; and a dosage is set to 4×10¹⁵ to 1×10¹⁷ ions/cm². In thisembodiment, implantation is conducted under the following dopingconditions: diborane (B₂H₆)/hydrogen (H₂) with diborane (B₂H₆) containedat an amount corresponding to a diborane (B₂H₆) dilution ratio of 5% isused; an acceleration voltage is set to 80 kV; and a dosage is set to2×10¹⁶ ions/cm² (see FIG. 16B).

Next, through the ashing process and washing with the organic solvent,the resist patterns 1034 to 1036 as a mask for the fourth doping processare removed. A first interlayer insulating film 1041 made of a siliconoxynitride film having a thickness of 150 nm is then deposited by aplasma CVD method. Following this, for thermal activation of an n-typeimpurity (phosphorous element) or a p-type impurity (boron element)doped into the semiconductor layers 1004 to 1008, heat treatment isconducted in an annealing furnace at 600° C. for 12 hours. The heattreatment concerned is performed for a thermal activation process of then-type or p-type impurity. In addition, it is performed in order togetter the catalytic element (nickel element) existing in the channelregion directly below the gate electrode by the above impurity as well.Here, the above thermal activation process may be performed before thedeposition of the first interlayer insulating film 1041, but when awiring material for the gate electrode etc. is low in heat resistance,it is preferable to perform the process after the deposition of thefirst interlayer insulating film 1041. Subsequently to the above heattreatment, in order to terminate dangling bonds in the semiconductorlayers 1004 to 1008, a hydrogenation process is performed at 410° C. for1 hour in a nitrogen atmosphere containing 3% of hydrogen (see FIG.17A).

Next, on the first interlayer insulating film 1041, a second interlayerinsulating film 1042 made of an acrylic resin film having a thickness of1.6 μm is formed. The above acrylic resin film can be formed by applyingit by a spin-coating method, followed by heat treatment in anoven-baking furnace. Subsequently, through the generally usedphotolithography and dry etching processes, contact holes 1043 with apredetermined size are formed so as to pass through the secondinterlayer insulating film 1042 and the first interlayer insulating film1041, and further the gate insulating film 1018 made of a silicon oxidefilm as a lower-layer film. Note that, the contact holes 1043 are formedso as to connect with the high concentration impurity regions (n⁺regions) 1026, 1028, and 1030 doped with an n-type impurity and the highconcentration impurity regions (p⁺ regions) 1037 and 1039 doped with ap-type impurity, and further a source wiring electrode 1017 cd(consisting of the first-layer source wiring electrode 1017 d and thesecond-layer source wiring electrode 1017 c) functioning as a sourcewiring (see FIG. 17B).

Next, conductive metallic wirings 1044 to 1049 are formed so as toachieve an electrical connection with the high concentration impurityregions (n⁺ regions) 1026, 1028 and the high concentration impurityregions (p⁺ regions) 1037 of the driver circuit 1106. Also, connectionelectrodes 1050, 1052, and 1053 and a gate wiring 1051 in a pixel region1107 are formed using the same conductive material. In this embodiment,as a material for forming the metallic wirings 1044 to 1049, theconnection electrodes 1050, 1052, and 1053, and the gate wiring 1051, alamination film of a Ti film having a thickness of 50 nm and an Al—Tialloy film having a thickness of 500 nm is employed. The connectionelectrode 1050 is formed so as to electrically connect the highconcentration impurity regions (n⁺ regions) 1030 and the second-layersource wiring electrode 1017 c serving as a source wiring. Theconnection electrode 1052 is formed so as to electrically connect withthe high concentration impurity regions (n⁺ regions) 1030 in the pixelTFT 1104 and the connection electrode 1053 is formed so as toelectrically connect with the high concentration impurity regions (p⁺regions) 1039 of the storage capacitor 1105. Also, the gate wiring 1051is formed so as to electrically connect the plural second-layer gateelectrodes 1015 c of the pixel TFT 1104 with each other (see FIG. 18A).

Next, a transparent conductive film made of an ITO (indium-tin-oxide)film etc. having a thickness of 80 to 120 nm is deposited and then, apixel electrode 1054 is formed through photolithography and wet etchingprocesses. The pixel electrode 1054 is electrically connected with thehigh concentration impurity region (n⁺ region) 1030 functioning as asource/drain region of the pixel TFT 1104 through the connectionelectrode 1052 and further electrically connected with the highconcentration impurity region (p⁺ region) 1039 of the storage capacitor1105 through the connection electrode 1053 as well (see FIG. 18B).

Through the above steps, an active matrix liquid crystal display devicehaving the n-channel TFTs 1101, 1103 and the p-channel TFT 1102 of aGOLD structure, and the pixel TFT 1104 of an LDD structure can bemanufactured. In the steps of forming the gate electrode, the storagecapacitor electrode, and the source wiring electrode of the above activematrix liquid crystal display device, there is adapted a dry etchingstep of one-step process or two-step process using an ICP dry etchingapparatus. This makes it possible to solve the problems inherent to theprior art in the dry etching step, that is, problems concerning, forexample, decrease in throughput in the dry etching step and increase inprocess cost resulting from consumption amount increase of etching gas,and further decrease in yield of a semiconductor device resulting fromthe complicated dry etching step.

As described above, the manufacturing method for the active matrixliquid crystal display device including a semiconductor device havingthe TFT of a GOLD structure has been specifically described, but thepresent invention can be modified in various manners without departingfrom the gist thereof. Needless to say, the present invention isapplicable to, for example, a manufacturing method for an active matrixorganic EL display device including a semiconductor device having a TFTof a GOLD structure.

EMBODIMENT 2

In this embodiment, a description will be made on a specific example ofan electronic device incorporating the semiconductor display devicemanufactured by applying a dry etching method less in process steps toprocessing on the gate electrode of the semiconductor device includingthe TFT of a GOLD structure. As the above semiconductor display device,there are an active matrix liquid crystal display device, an EL displaydevice, and the like. The semiconductor display device is applied to adisplay portion of the various types of electronic devices. Here,specific examples of the electronic device in which the semiconductordisplay device is applied to its display portion are described withreference to FIGS. 19A to 21C.

Note that, examples of the electronic device in which the semiconductordisplay device is applied to its display portion include a video camera,a digital camera, a projector (rear type or front type), a head mounteddisplay (goggle type display), a game machine, a car navigation system,a personal computer, and a portable digital assistant (mobile computer,cellular phone, electronic dictionary, or the like).

FIG. 19A shows a personal computer composed of a main body 1201, a videoinput portion 1202, a display device 1203, and a keyboard 1204. Thesemiconductor display device of the present invention is applicable tothe above display device 1203 and other circuits.

FIG. 19B shows a video camera composed of a main body 1301, a displaydevice 1302, a voice input portion 1303, operation switches 1304, abattery 1305, and an image receiving portion 1306. The semiconductordisplay device of the present invention is applicable to the abovedisplay device 1302 and other circuits.

FIG. 19C shows a mobile computer composed of a main body 1401, a cameraportion 1402, an image receiving portion 1403, an operation switch 1404,and a display device 1405. The semiconductor display device of thepresent invention is applicable to the above display device 1405 andother circuits.

FIG. 19D shows a goggle type display composed of a main body 1501,display devices 1502, and arm portions 1503. The semiconductor displaydevice of the present invention is applicable to the above displaydevices 1502 and other circuits.

FIG. 19E shows a player for a recording medium having a program recordedtherein (hereinafter, simply referred to as recording medium), which iscomposed of a main body 1601, a display device 1602, speaker portions1603, a recording medium 1604, and operation switches 1605. Note that,this device employs a DVD, a CD, etc., as a recording medium, which canbe used for music appreciation, a game, or Internet. The semiconductordisplay device of the present invention is applicable to the abovedisplay device 1602 and other circuits.

FIG. 19F shows a cellular phone composed of a display panel 1701, anoperation panel 1702, a connecting portion 1703, a display portion 1704,a voice output portion 1705, operation keys 1706, a power switch 1707, avoice input portion 1708, and an antenna 1709. The display panel 1701and the operation panel 1702 are connected with each other in theconnecting portion 1703. The angle θ made by a plane where the displayportion 1704 of the display panel 1701 is positioned and a plane wherethe operation keys 1706 of the operation panel 1702 are positioned canbe arbitrarily changed in the connecting portion 1703. Note that, thesemiconductor display device of the present invention is applicable tothe above display portion 1704 and other circuits.

FIG. 20A shows a front-type projector composed of light source opticalsystem and display device 1801 and a screen 1802. The semiconductordisplay device of the present invention is applicable to the abovedisplay device 1801 and other circuits.

FIG. 20B shows a rear-type projector composed of a main body 1901, lightsource optical system and display device 1902, mirrors 1903 and 1904,and a screen 1905. The semiconductor display device of the presentinvention is applicable to the above display device 1902 and othercircuits.

Further, FIG. 20C shows an example of a structure of the light sourceoptical system and display device 1801 shown in FIG. 20A and the lightsource optical system and display device 1902 shown in FIG. 20B. Thelight source optical system and display device 1801 and the light sourceoptical system and display device 1902 are each composed of a lightsource optical system 2001, mirrors 2002 and 2004 to 2006, a dichroicmirror 2003, an optical system 2007, a display device 2008, aretardation plate 2009, and a projection optical system 2010. Theprojection optical system 2010 is composed of a plurality of opticallenses provided with the projection lens. This structure is called a3-CCD system because the three display devices 2008 are used. It ispossible to appropriately arrange an optical lens and a film having apolarization function, a film for adjusting a phase difference, an IRfilm, or the like in some midpoint of an optical path indicated by thearrow of FIG. 20C.

FIG. 20D shows an example of a structure of the light source opticalsystem 2001 shown in FIG. 20C. In this embodiment, the light sourceoptical system 2001 is composed of a reflector 2011, a light source2012, lens arrays 2013, 2014, a polarization conversion element 2015,and a condensing lens 2016. Note that, the light source optical system2001 shown in the figure is only employed as an example. Needless tosay, the system is not limited to the above structure. For example, itis possible to additionally provide for the light source optical system2001 the optical lens and the film having a polarization function, thefilm for adjusting a phase difference, the IR film, or the like asappropriate (see FIGS. 20A to 20D).

FIG. 21A shows an example of a single CCD system. Light source opticalsystem and display device shown in FIG. 21A is composed of a lightsource optical system 2101, a display device 2102, a projection opticalsystem 2103, and a retardation plate 2104. The projection optical system2103 is composed of a plurality of optical lenses provided with aprojection lens. The light source optical system and display deviceshown in the figure is applicable to the light source optical system anddisplay device 1801 of FIG. 20A and the light source optical system anddisplay device 1902 of FIG. 20B. Also, the light source optical systemof FIG. 20D may be used for the light source optical system 2101.Further, the display device 2102 is additionally provided with a colorfilter (not shown), which enables a color video display.

Light source optical system and display device shown in FIG. 21B is anapplication of that shown in FIG. 21A, to which a rotation color filterdisc 2105 of RGB is applied to achieve the color video display insteadof additionally arranging the color filter. The light source opticalsystem and display device shown in the figure is applicable to the lightsource optical system and display device 1801 of FIG. 20A and the lightsource optical system and display device 1902 of FIG. 20B.

Light source optical system and display device shown in FIG. 21C iscalled a color-filterless single CCD system. In this system, a microlensarray 2115 is additionally provided in a display device 2116, to which adichroic mirror (green) 2112, a dichroic mirror (red) 2113, and adichroic mirror (blue) 2114 are applied to achieve the color videodisplay. A projection optical system 2117 is composed of a plurality ofoptical lenses provided with a projection lens. The light source opticalsystem and display device shown in the figure is applicable to the lightsource optical system and display device 1801 of FIG. 20A and the lightsource optical system and display device 1902 of FIG. 20B. Also, anoptical system using a coupling lens and a collimator lens in additionto the light source may be applied to a light source optical system 2111(see FIGS. 21A to 21C).

As described above, the present invention can be implemented in anextremely wide application range thereof and applied to variouselectronic devices incorporating the semiconductor display device suchas an active matrix liquid crystal display device or an EL displaydevice.

Effects of the present invention will be cited below.

As a first effect of the present invention, the invention is effectivein improvement of the throughput in the dry etching step.

As a second effect of the present invention, the invention is effectivein reduction of a consumption amount of the etching gas.

As a third effect of the present invention, the invention is effectivealso in improvement of the yield of the semiconductor device bysuppressing defects and troubles in association with a simplified dryetching step.

1. A method of manufacturing a semiconductor device, comprising: formingan island-like semiconductor film over an insulating substrate; forminga gate insulating film comprising an oxide film on the semiconductorfilm; forming a first-layer gate electrode film comprising one oftantalum nitride and tantalum on the gate insulating film; forming asecond-layer gate electrode film comprising one of tungsten, a compoundcontaining tungsten as a main constituent, and tungsten nitride on thefirst-layer gate electrode film; forming a mask on the second-layer gateelectrode film; and performing an etching process to such a degree thatthe gate insulating film is exposed and the second-layer gate electrodefilm is shorter in the size in a channel direction than the first-layergate electrode film by using etching gas containing fluorine gas,chlorine gas, and oxygen with a predetermined chamber pressure, ICPpower density, bias power density, and flow ratio of the fluorine gas,the chlorine gas, and the oxygen. 2-21. (Canceled)